Character A is living a normal life in their normal town, doing normal things, until their abrupt and tragic death. When they awake, however, they find that they have reincarnated as a character in a book/game they've read/played recently! And not only that, but the character that they've reincarnated as is the villain, who meets a horrible and just end at the hands of the hero, Character B?! Can Character A turn their luck around and live a decent (and hopefully long) life, or are they fated to be destroyed in the end regardless of what they do?
(This story could be set in a school setting, modern setting, historical fantasy or a game world)

Character A, after suddenly dying, finds themselves in the world of a novel they recently read. A thrilling plot about romance, danger, suspense and mystery! Only the problem is... They've been reincarnated as a side character, who is supposed to die in the first chapter to bring the two romantic leads together. A bitter, short life as cannon fodder is what awaits them?! No way! Using their wits, skills, knowledge of the plot and maybe a thing or two they remember from their previous world, Character A evades death and catches the eye of the lead, Character B. But now that the flow of fate has changed, will things still happen as they did in the novel? And why does a side character like them keep finding themselves in the midst of danger?

After reincarnating/transmigrating, Character A finds themselves in the world of a dating sim romance game that they played while living in their previous world. Unlike some unlike losers who might be reincarnated as side characters or villains, Character A is the heroine! A beautiful, intelligent young upstart who manages to charm her way into the hearts of the dateable characters in the magical school setting she's in. The only thing is... Character A never really liked these kinds of games, and was way more interested in the monsters and dungeons mentioned in the game. Ignoring the catty noble girls, the expectations of proper ladies, and the dateable leads, Character A decides to instead become a dungeon crawling monster hunter! The only problem is, they've somehow attracted the attention of the notoriously difficult to woo and extremely popular Character B. Can Character A survive an explosive school drama turned on its head and become the adventurer they've dreamed of?

Character A is a fighter pilot in the Galactic Directorate, currently embroiled in the midst of a bitter civil war. During a space battle, a mysterious plot-compelling wormhole (a plothole, one might say) pulls their ship through space and causes it to crash land on a distant planet, far out of known space. Thankfully, the planet has a breathable atmosphere, plenty of water and vegetation, and is even populated by an extremely human-like race. Ejected from their spaceship and with only the bare essentials on them, Character A leaves their pod to discover that they've killed one of the high-ranking noble inhabitants of this planet in the crash. Who happens to look exactly like them. Panicking about the potential for a diplomatic disaster and the consequences, Character A winds up impersonating their dead doppelgänger, feigning amnesia and entering an engagement with royal successor Character B in their stead. With the technological advancement of the planet being medieval in comparison to their own, their only means of getting off the planet would be to find their spaceship and repair it. Can they avoid suspicion while pretending to be someone they aren't? Were they the only ones to crash on the planet? How long will they survive without indoor plumbing and toaster strudels?

The war with the demons may have started abruptly, but it lasted 20 years. Character A is a 40-50 year old summoner and veteran of this war, capable of binding spirits and demons alike to use their powers and forms in battle. However, their mana was weak, and in exchange to grow their mana pool, they were forced to undergo a ritual that greatly disfigured them and caused their every waking moment to be filled with pain. Not only that, but their accomplishments in war and their reputation as a summoner was stolen by their cruel fiancé and commander, the Golden Knight, who has abused and ridiculed them every step of the way. Now, on the eve of the celebration banquet, with no further need of their powers, A is left to die alone in agony. Bitterly resenting themselves and the way their life turned out, Character A curses themselves for their foolish mistakes which let them be led astray and betrayed and left with a broken body. Just before the moment of death, however, a blinding rush of light envelopes the world, and Character A discovers that they are mysteriously in their body as it was 20 years prior. Time has been turned back, but Character A seems to be the only one who remembers the events of the future? The demon invasion has yet to begin, and they've just been proposed to by their wicked fiancé. Determined not to let the same events happen twice, Character A strikes up an alliance with the Golden Knight's fiercest rival, Character B, and begins making preparations for the war only they know is coming. But what caused time to reverse itself? Is Character A the only one who remembers the previous timeline? And why are the events leading up to the invasion happening much sooner than they should have?
(Can take place in a modern, steampunk, or medieval setting)

Working a boring office job by day and writing fiction by night, Character A is the author of the highly popular Prince series, a collection of novels about the underdog princes of a fantasy empire overcoming hardship and finding love, wealth, status, and true happiness. One day, however, they find that their apartment has been broken into by none other than Character B, the Forgotten Prince and villain from their series! Angry at their destiny and mishaps, Character B abducts Character A by bringing them to their world, the world of the novel, and demanding that they write him a happy ending where he becomes emperor. However, A's writing magic only seems to apply to themselves, and the only way to change the story is to write from the outside world! Striking a deal, A and B agree to work together to return A to their world in exchange for B's happy ending. But the world is beginning to change from how A originally wrote it. Monsters they never wrote or imagined are suddenly appearing and causing havoc? Strange earthquakes and natural disasters in an otherwise peaceful land? Important political figures A never wrote about are seizing control of the nation, and most disturbing is; A's former protagonists are acting completely out of character! What has happened to their beloved story world?
(The role of Character B is genderlocked to male. Thus this story can only be either MxM or FxM)

Character A is the Demon Lord, preparing to invade the mortal realm as the hour of the prophecy draws near. The demon world is dying, its World Tree has withered, and its inhabitants have been rejected from the human realm out of prejudice and fear. Thus, the council of elders has decided that the only hope demonkind has is to invade and conquer the human realm! Just before A is about to give their speech declaring war, they suddenly recall their memories of their past life. This world is the world of a game they played, and they are the ultimate boss villain, who is killed by the hero in the final battle, restoring peace to the human land.

Unwilling to die after their first short life, but not wanting to sacrifice their people, Character A remembers the epilogue quest after the game has been cleared; the war with the humans endangers the fate of the human world and causes it to die, so the Hero goes on a quest to retrieve the Sap of Yggdrasil, a legendary item that can revitalize barren lands and save a world's World Tree, preventing its destruction. Hiding their magical powers and disguising themselves as a human, Character A escapes to the human world alone to find the sap, save their world, and avoid their untimely death. However, by sheer coincidence, they run into the hero, Character B, while saving some travelers from a monster in the game's opening sequence. Stuck with the person they least wanted to see, Character A has to hide their identity and purpose from Character B, and somehow becomes a party character? This wasn't supposed to happen! Can A still save their world and their life without B finding out who or what they are?