Of course, some characters wouldn't have that much dramatic reactions, but others would feel very strongly. I read real people's accounts that describe crippling guilt, and it's hard to imagine what they are going through to be able to write it.

This will obviously differ from person to person, and in the cases of people with certain types of psychological conditions it might have no effect at all, or a reverse effect, but overwhelming guilt is often a big point, yeah.

A recurring point in terms of physical description seems to be that the rule of thumb is that if they did it with a weapon then a good way to portray it is to have them shaking to the point that this weapon, say, a gun for example, is almost uncontrollable in their grasp, so they either look like it could drop at any moment, or they could have to have it pried from their hands by someone. Showing the person has virtually been paralysed by the shock of what they've done can also help, and sometimes they're portrayed as spacing out to the point that people speaking to them have a hard time getting through. I think extreme shock is usually a good sign, and this is often shown by the person trembling uncontrollably. Another common portrayal is to have the person actually throw up after the killing happens, to emphasize how sick and nauseated it's making them.

Never killed anyone myself, so can't comment from realistic experience here. Mostly just giving what I frequently see as the way of portraying such an emotion, and using some of my understanding of human psychology. There's usually guilt, but how people handle it is different. Some people could become overwhelmed by that emotion and go into severe shock, while others might become traumatized in a way that makes them go completely dead silent. I don't think anyone will be able to give you a perfect way to write this unless they had personal experience, and even then it would just be a subjective situation; how they handled it and not immediately appropriate to everyone.

Internally, crippling guilt is a good start. This guilt can often lead to questions like "What right do I have to be alive?", "Why is my life more deserving to continue than theirs?", etc. Taking another life can also cause a person to have to come to terms with how fragile life actually is, which might change their perspective of life, death, or even the world depending on how severely it effects them. Some might come to realize their own mortality as a result, if they had never really approached the idea of dying themselves before.

I'm multitasking pretty badly right now, but if more comes to me, and chances are it definitely will once I'm able to think about it clearly, I'll either post again (*shock*double post*shock*) or I'll edit this.

My character Kat was so badly affected that she suffered penalties to her attack rolls (FATE game, milked that for fate points <3). She was a thief, and she'd fight, but she'd never killed anyone up close and personal (she'd possibly gotten the final shot with a gun, but I think in the heat of a battle she might not notice them go down and might not know they're dead, not just injured).

My character Raia was...not happy, but she has a very strong moral and ethical compass, and she saw that person as wicked. She handled it well, though she had a few nightmares after.

Max has an interesting story. He's actually a sworn pacifist, and it's magically enforced (side effect of the holy healing magic he's been granted. He's a doctor). However before he received that boon, he was possessed and attacked someone. He didn't remember that, but found out after the fact. Then he was stuck in a dimension that responds to fears, so he had to watch himself do it over and over....that whole series traumatized him quite a bit. However, the first person he actually killed was a matter of a cancer patient who was in a great deal of pain and didn't have long to live anyhow. She wanted him to, so he used anesthetic to send her on her way. The two were good friends, and he was shaken and upset, but not significantly more than he would have been by her death in general.

I agree with everything @Shoryu Magami has said. Another thing that might happen is nightmares, as I mentioned, or perhaps the image of that final blow replaying over and over in their head, either right away, or in similar situations.

There is, however, the other side of the coin. Some people like killing, it gives them a rush. For whatever reason, perhaps the character is excited. A thrill of adrenaline, a surge of satisfaction...not a happy thought, but a possibility. There's also some who wouldn't even care. The other guy's dead, so what. Or maybe because it's "them or me" it doesn't bother them.

Hatred of the cause that resulted in that situation ending in the kill is another idea. It's always easier to blame someone else. Perhaps a soldier hates a country or a government that sends people off to fight while sitting safe at home in peace. Perhaps a homeless person hates the system that forces him to steal to survive, and how he wouldn't have been trying ot rob that store if he could just get a job. Why does nobody understand how hard it is? Why do they all think it's just a matter of trying harder? In an extreme case, the killer may end up cynical and jaded, a pessimist, and even hate humanity as a whole.

Since @shylarah brought up some of the other points I would've mentioned if I had gone further into it earlier, I might as well make another post instead of edit the previous one like I said I might. They did a good job bringing up some of the elements that I mentioned when I said certain type of psychological conditions might cause it to have no effect at all, or a reverse effect. Since the original poster seemed to be planning on writing from the context of them actually feeling guilt, I tried to focus on those aspects of the experience.

Certain types of psychological conditions, such as if the character is a psychopath, would have an impact on how they experience the act. These types of people usually lack the capacity for any sort of concept of morality or genuine feeling towards others. They are fundamentally self-centred people who view the world in a very superficial way, though they are often very good at pretending to be capable of the depths they completely lack. They never understand the feelings of other people on anything more than an intellectual level (they understand the words but not the soul) and lack empathy, and usually always view the worth of others based on whether or not those people are useful to them. Many of them are able to commit murders or torture others with the same level of ease and apathy that they would experience from mundane activities like brushing their teeth.

While some people will exhibit this sort of detached behaviour to the experience of killing another as a defence mechanism to deal with the shock and guilt, people like this will openly feel nothing about what they did, or may even just rationalize it as "kill or be killed", "survival of the fittest", or some other way of trying to use logic to detach themselves from the more emotional and moral elements of what happened. This sort of mind state where they fail to acknowledge the act of killing as important is definitely the sort of mentality that a large amount of military training brainwashes into people, or those who become contract killers, and it's not entirely common for people to merely look at the lives of others as numbers or statistics for some scientific experiment or self-serving materialistic agenda.

As they mentioned in the previous post, mentality's involving misanthropy, becoming jaded or cynical or pessimistic, or, as I'll now add, nihilistic ideologies and Machiavellian perspectives of the world, will result in a similar type of total indifference towards the events of taking another person's life, and in some of their cases they may even come to enjoy it. In some other people's cases, they will so often that they actually get used to it, again resulting in apathy and nonchalance about their acts. Since you seem to be writing from the perspective or someone who has done it for the first time though, this is probably not what you had in mind.

People who come to hate other humans, or who exhibit qualities that have been mentioned by me and the previous poster will also, as stated, have the possibility to create a person who actually enjoys killing others, and certain types of other personality traits such as being a sadist can have the same sort of effect. A lot of people also kill out of lust, but, I noted, the topic is based on the idea that the person is more conventional in their reaction to death and is also doing it for the first time, so some of these answers aren't what you want. People could become consumed by bloodlust or excitement about the events for a number of reasons, so it's not, as they said, impossible that they will experience it positively. They could also not care, as the previous poster said, for a variety of reasons other than those I mentioned.

It's not pretty, but it's nature. This likely isn't what you have in mind though.

It's important to note here (as @Shoryu Magami touched on) that military training has an impact on this. Modern military training specifically is designed specifically to make you shoot first and think later. Nowadays, if you're in the Army with a gun and you come across and enemy, you'll fire on instinct. In WWII, however, MOST of the soldiers wouldn't even pull the trigger. This goes all the way back to the invention of the musket, where the accuracy of fire reduced rapidly in actual combat due to the simple fact that these people were staring other humans beings in the eye and consciously or unconsciously threw off their own shot. There are plenty of stories of opposing forces meeting during these time periods and simply walking past each other. One case from one of the world wars involved small groups of British and German forces meeting along a road. Instead of opening fire, they laid down their weapons and started throwing rocks. Lindybeige (my personal favorite military/history nerd channel) actually has a video on this specifically and touches on how it can affect reactions to killing (briefly, if I remember right, but he still touches on it).

Yep, @Keyguyperson has basically gone into more detail on exactly what I was implying with that last comment of mine, and cool to see a mention about how in the those wars the opposing sides often ended up more or less interacting with one another. I've even seen information about how during cease fires both sides would actually eat together, though I wasn't given citation on that particular detail.

Dehumanizing the enemy to the point where the soldiers no longer actually acknowledge that they are shooting at people just like them, or simply conditioning them with training to pull the trigger instinctively without even questioning the situation, is precisely how military works in the modern era. As science progresses, so does the understanding of how to brainwash people, which is why the way the military can control people like this developed. A lot of propaganda and media is also centred around facilitating this need for people to view the other side as something that isn't human, subsequently removing the effects killing them will have on the psyche.

Similarly, governments will make enemies out of nothing in order to start wars over materialistic agendas, not just ones rooted in prejudice or hatred, creating all sorts of justifications for why the enemy is the enemy and why you're a traitor if you don't fight the enemy. These people will never have to watch the people who die as a result of those conflicts they've instigated; the ordinary men and women and children will. This is another example of how becoming detached to things is the beginning of the end for someone having any semblance of being a real human.

Someone also doesn't need to see the thousands of people whose lives were taken by a nuclear weapon when compared to, say, seeing the person you shot with a gun, and guns are also largely varied with how much you need to actually see the person when they are killed. For example, a sniper can usually see their target in very vivid detail through a scope, so this type of person is more likely to be effected by having to shoot these people, though, like we've already said, the military does actually more or less drill out this tendency to think about what you're doing or feel anything about it, so the soldier is mostly operating on instinct at that point, or like a machine.

In earlier times it was a lot more difficult to condition soldiers to act this way, regardless of what culture or country they were part of, because weapons were significantly less impersonal and you were always forced to accept that this was someone just like you. It takes a whole lot more conviction to make yourself cut someone's whose looking you in the eyes down with a sword then it does to shoot someone whose basically a dot far away in the distance. This is why people usually had to believe they were fighting for a very good cause to be willing to kill like this, whereas other life forms will just kill out of instinct. Humans generally need a justification to ignore their conscience, but brainwashing can force your conscience to be locked away.

On the flip side of this though, and more focusing on what I believe to be the primary purpose of the original poster's question (how to write someone who handles taking a life for the first time badly), there are also countless stories of soldiers who have become shell shocked because of all the lives they had to take or all the death they had to witness. While nowhere near the same scale as the original poster's scenario of a single person taking the life of a single other person, it still shows the immense scarring that a person with a more tangible conscience, and general sense of morality and empathy, will go through from killing another.

@Shoryu Magami @Keyguyperson I thought about mentioning nihilism but I wasn't sufficiently sure of the meaning. ^.^; I went more into different reactions because Shoryu solidly covered most of my guilt responses. And yep, perhaps the most famous instance of cease-fires is the Christmas truce of...1943? Some time in WW2. It's mentioned in a wide variety of places, including a song by a favorite folk artist of mine. However, based on books and stuff I read, even trained soldiers can experience guilt and so on, though with a gun in war it often is delayed a bit (like until the first time they have a chance to think about it). It's a shame that guns make killing so much easier, in more than one sense of the word. It takes a whole lot more effort to kill a guy with a sword not just because you might not get him as well, but also as Shoryu said, because you have to look him in the face while you do it.

You just made another good point about that as well, @shylarah; not having time to think about it in the first place. With the implementation of more advanced weaponry, fights became progressively more chaotic. Sure, it's chaos on the battlefield no matter what, and I'd be lying if I said thousands of troops wielding swords or spears wouldn't have to be constantly on their toes and focused almost exclusively on survival, but when guns get introduced into the scenario... people die in a split second. Since people are usually brainwashed, or at the very least pressured or obligated in older days, to instinctively kill without hesitation, they only get ruined by what's happened after the fact.

No problem about not going into nihilism. I'm always happy to touch on anything heavily rooted in philosophy or psychology because they're some of the fields I specialize in. Nihilism is definitely a very large contributing factor for why people develop psychological conditions that would lack morality or empathy, but, unfortunately, it's also a big cause of people who don't even have these problems ending up developing a mentality that facilitates killing or hurting others, or at the very least not caring about the death or suffering of others. If you view the world as a meaningless place with no value and no true concept or good or evil, and view life as just a pointless single flash in a universe that is largely nothing but death, you very quickly lose the ability to care about anything.

"There's no meaning in this world, and there's no such thing as good or evil, so we might as well go out with a bang and have fun killing people since their lives mean nothing." is one of the most malevolent states of mind a person can end up developing, and it's basically the dark extreme of nihilism that so many fictional villains have tried to represent. It's always important to remember, however, that these fictional characters are representing a very possible mind state a person can develop. There are very harsh consequences for people neglecting the deeper and more meaningful facets of the human mind and conscience.

In my experience this can vary so much depending on the character structure and the design of the roleplay. Some are simply immune to such horrors and sadly those ones have to be played out like the hero of an action movie; killing people like pawns on a battlefield. For me, this is less fun as I like to play around with the emotional impact that it can cause and the trauma inside the character's head. (Just take a look at my Madison character when I had her wake up after an amputated arm and an eye removal)

As someone who has suffered from some serious anxiety and depressive stages in my life (Don't ask for shits and giggles unless you really wanna know... but they got pretty bad) I find can utilise these as an understanding for what a character may feel. It's not going to be along the same vein, but death is disturbing and it affects the people involved in very similar ways. Adding things like relapses, failure to perform simple tasks, loss in concentration on a task at hand and altering the character's emotions all contribute to that helpless feeling that they may be feeling.

It also depends if its accidental or on purpose...

• Accidental:
  Can appear as someone that will instantly tend to the person in the hopes of righting what is wrong and what they essentially fucked up. The character will often feel as if they should be the one to die instead and will possibly wish that they were the one that died instead.
• On Purpose:
  This will depend on whether it's the first death or not. Hotline Miami actually showed this off in the best way during the first few scenes. The main character, Jacket, just killed a whole bunch of people with no remorse but then kills an innocent homeless guy. Upon walking away he stops and spews on the ground, showing that he feels a deep sickness for what he has done.
  As the character moves on they could become more and more violent or start to suffer from symptoms like PTSD, flashbacks and/or nightmares.

Again, this is all based on a bit of a black and white view, but you can have someone that is a killer on purpose and suddenly relapses into regret. Pretty much if you can fuck around with the character's mental side and break them down into nothingness, then you might be doing something right.

(I've made a point of this in a few places on the site now, but just you know here too, my internet has gone down due to some undefined screw up on the part of my ISP, meaning that I had to blow money on a mobile dongle just to be able to communicate with people about it and try to solve the issue. This also means that, while I'm posting here right now, I'll run out of data eventually and I'll have no real idea when it'll happen, and from that point on you guys won't hear from me at all until the issues with my ISP are solved.)

@NuttsnBolts pointed out some more useful thoughts about how the setting itself will cause an impact on it. This doesn't just apply to fictional circumstances either, but real situations too. A person who lives in a world where death is a constant thing around them all the time is most likely going to be desensitized to it all, which will have an effect on how they take killing someone. In those kinds of situations, they might still be hit hard by it, or they might just not feel much of anything because it's too "ordinary" for the life they have come to know all around them. Some people are immune the effects of killing for other reasons as well, such as the mentality a contract killer or a soldier will develop if it doesn't all build up and break them inside. These sort of examples don't really apply to the topic point of killing for the first time though.

Given how I know what severe depression and anxiety is like (I won't explain), I also agree that some of the symptoms they mentioned there are possible effects if they don't handle killing someone well.

The points made about whether or not it was on purpose or not also definitely have a contributing factor, yeah, and another thing which can play a part in how the person handles it, other than their own personal mental state and psychological conditions, is if they did it to defend themselves or if it was a premeditated kill. Like I said before, doing it to defend themselves can sometimes lead to the "kill or be killed" train of thought that causes them to brush what they did off, though this might not allow them to brush it off if they realize that even in a really bad scenario they still had free will and could have looked for a way out of the situation without actually killing the enemy. A person whose actively gone in for the kill and murdered someone won't be able to just brush it off like this, though they still might pass it off as "survival of the fittest"; in fact some people/characters actually justify being murderers this way.

Entirely depends on the character, and why they killed the person.

In complete self-defense, a brief mixture of guilt and triumph.

As an accident, large portions of worry at first, but then switching to guilt and fear.

In revenge, there would be some satisfaction at first, followed by a cold empty feeling.

In cold blood, very little would be felt other then some insane rantings within the mind. Perhaps some mild satisfaction as well.

In an uncontrolled rampage, extreme guilt.