Yep, you've got the gist of it. There are numerous angels and demons available for contracting, many with unique and varied powers like the examples you mentioned. Funnily enough, you managed to hit on the exact two powers that have lore relevance to this story. One of the seven Ascended demigods possesses the power to reverse time by a limited amount, while it was a war against a Void demigod (shapeshifter type) that ultimately drove Regret to ascend. So yeah, there's absolutely all kinds of demigod spirits to contract with.

What makes Ascendants like Regret stand out from all the rest is that they are the only ones with mortal forms. As such, Regret is the only demigod you can contract with whom you can actually see in person with your own eyes.

You mentioned our characters memories with Regret are lost. Then, have they also absolutely zero recollection of their previous life initially?

Do they they regain their memories over time? Or does it vary case by case, maybe even depends on whether they try to remember or other factors?

When did Regret become involved with Aetherion, when she was still human or afterwards?

Does she consider it 'her' kingdom/does she show it preference?

How influential is she as a demigoddess?

I take it Yddrog is an unusual exception as a contractor in how much he can defy his patron (and creator)? Is that because Regret was too lenient in their contract, gave him too much power for 'free'? Or did he also manage to rebel because of his innate will?

@SilverPaw
Ooh. I'm liking this character already. I think you've got a knack for this. Wanna make him a former king of Aetherion? If we're looking to make the state of his kingdom uncertain, perhaps his domain is a smaller nation that got absorbed into the larger kingdom. Maybe his kingdom joined an alliance which later transitioned to a state within Aetherion's constitutional monarchy. Or, perhaps a war broke out that got his kingdom conquered and absorbed, whether by Aetherion or by a rival state.

For a more tragic scenario, maybe the entire domain fell under Yddrog's rule, its human population enslaved and replaced with monsters or allied mortal races (like orcs). Perhaps one small, dwindling human settlement remained in hiding within a cave, and Yddrog could throw the prince a bone by giving him authority over the settlement. Maybe something like, "As long as you can procure me a pure maiden to sacrifice every ten years, I see no reason not to allow their pitiful existence. What a generous ruler I am, yes? Feel free to thank me."

@Zyx@SilverPaw
I just had a eureka moment: if we go with the tragic second-paragraph plotline, what if Zyx's character was a citizen of SilverPaw's kingdom, perhaps even the king's bodyguard, brother, or friend? Because, for someone to feel such an intense level of vindictiveness against the gods and conviction in the betterment of humanity, I imagine something incredibly tragic must have happened to them and the people around them. The demigod Yddrog slaughtered everyone he ever loved, and the demigod Regret was the one who created him. And lest one think that the other patrons are more acceptable, perhaps Yddrog's mages were responsible for the devastation. That kind of experience might cause anyone to swear off all demigods entirely - and drive him toward Regret in search of power and time to exact his revenge.

Just an idea.

Edit: If we want to cut down on the tragedies and go for a more upbeat tale, then the first-paragraph plotline of the kingdom joining the alliance opens up a different set of possibilities. People don't always need to experience tragedy before they'll feel a strong conviction for something. Oftentimes, a really good upbringing will do that just as well. Perhaps Zyx's character did extraordinarily well in life; maybe he was a commoner who got rich enough to buy into nobility, or an inventor who managed to change the world, or even just a priest who, after having met thousands of good, strong people in his life, learned the rich wellspring of strength that humans were capable of without demigods to support them.

Which brings me to a question: do you have a story idea in mind for your character, Zyx?

@Zyx
Enslaving the gods, eh? I look forward to seeing how he pulls that off. I imagine some contract shenanigans would be involved, like some expertly worded fine print that backfires on the patron at some point. If you can get your hands on a Bane weapon, it may be possible to kill the patrons outright. True Bane weapons are blessed by the gods, like actual highest-level gods (i.e. beyond demigods), to condemn to the afterlife whoever receives of them a mortal wound, regardless of any other mortality considerations. So if you were to smite a demigod's avatar with it, their soul would immediately lose all its authority and gravitate to the afterlife, even if that individual would normally have the Divine Authority to live beyond death. Bane weapons are really only effective against higher beings, since mortals are already dragged to the afterlife upon death, so a Bane weapon wouldn't affect them any differently.

True Bane/Godbane weapons capable of indiscriminate slaughter of demigods are little more than a myth right now. However, Regret was able to create Demibane weapons from her own lifeblood capable of canceling the inherited immortality powers of her contractors. They only work on those empowered by Regret (though not on Regret herself). They're mandatory for killing Yddrog again, so the players will eventually get their hands on these. There's also a lesser version, Rot weapons, that cancel all cell division in the injured area and poison the target's body with enchanted Blood of Regret. Normally her blood would grant immortality to whoever it flows through, but she can flip its effect with an enchantment to sap life instead. The target will visibly age and rot away as the poison makes its way through their body. So anyone with unascended/biological forms of immortality, like vampires or zombies, will rapidly fall to this weapon.

Yddrog has his own equivalent, Dragonbane weapons, that can pierce any inheritor of Yddrog's blood by "commanding" it on contact to make way for the king. Take a wild guess who it's meant for! e_e