I Became the Villain's Little Brother

Yoru reads his own story in a mysterious book that he found. In his second life, where he has struggled alone since childhood and does not know his family, he finds a little comfort from reading various novels.

The novel titled Unrequited Love that he accidentally found in the park gives him a big surprise. The story of his first life is written there, but he only exists as a side character who ultimately dies midway through the story due to betrayal.

Recalling his mistakes in the first life in a different world, Yoru continues to reread the novel over and over to find the reason he had to suffer. Then, he realizes it.
The female protagonist, Elaine, is the cause. Yoru lost everything because of Elaine.

The old resentment that was buried starts to rise within him until he swears in his heart. If he could go back to his first life, he would make sure Elaine pays for her actions.

Or so he thought...

When he wakes up in confusion, he returns to his first world with the same name at the age of eight. Twenty years from now, he will die from a terminal illness.

What will he do to change his destiny in his first life?