Toaru Majutsu no Index - Volume 10, Chapter 6: Resumption of Pursuit with an End. Accidental_Firing.

Su Shuilian was the first legitimate daughter of a renowned embroidery family, but she was murdered by her jealous family member. After death, Su Shuilian’s soul enters an unknown female body who lives in a dynasty she had never heard of.

While trapped in the wilderness with her wolf pup companions, Shuilian picks up an assassin who was betrayed by his organization and saves him from the brink of death.

After making it out of the dangerous forest, the two travel to a small town with few inhabitants. There, they find a location with a picturesque scenery and disguise themselves as a married couple to buy a house to settle down in.

She was a girl unfamiliar to this world, and he was an infamous assassin. Journey with them as they adapt to their new life…

- Description from Novelupdates

I met the male lead in prison.

An F-Class Hunter.

A happy and fulfilled life, everyone wanted that. Rio was no exception, he too wanted to feel joy and fulfillment.

But how many actually achieved that?

He didn't know, but he knew that he was not part of those.

Rio, a part time editor of a webnovel called, The Last Stand, transmigrated inside the world of the novel. Not as a main character, nor as a villain, not even a student.

But as a professor.

A simple extra, professor that was never even mentioned in the story. Through some circumstances, he was the mentor of the main cast of characters.

Armed with knowledge of the future, treasures of the world, and skills of different origins. He would raise these students to their utmost as early as possible. He felt that there would be no problem.

However, as time marches forward he realizes everything was not as simple as he thought.

The plot, or the future, as he knew it was going further down the rails. The body he occupied had a mysterious identity. A higher existence watches over him.

Realizing the implications, he gave up on staying low key and unknown. He will strive, live, and survive admist this world of cruelty.

A world set in a modern futuristic setting where cults roam free, capitalism corruption rises, demons and other races exist.

However, even if he survived and lived, will he even feel happinness and fulfillment? He didn't know, but he will live still.