Re:Zero Kara Hajimeru Isekai Seikatsu - Volume 4, Chapter 10 [The Incarnation Of The Thirst For Knowledge]

In a parallel world filled with pet beasts, people tame, train, evolve, and trade beasts.

Grandpa Yu often repeated beside the ear of Yu Zhen, saying that he(YZ) has a soul in his body. If he doesn’t properly train in asceticism, and raise then send away the powerful soul, in this lifetime he would have to live as a bachelor. In his next lifetime he would be reborn as a lifestock animal.

Yu Zhen played on his mobile and nodded. On the surface he replied, “Uh-huh”. In his heart he laughed, “hahaha”. Keeping his grandfather in the dark was amusing so the lie was repeated for over ten years without Yu Zhen getting tired of it.

After some years, Grandpa Yu passed away and a cold-faced handsome guy came to his door in a luxury car – with a household register in his hands.

…..

Yu Zhen: The soul in my body reincarnated into someone else’s body to demand repayment, what should I do!

- Description from Novelupdates

It all started when a minute before we began morning activities, something suddenly occurred. The floor started shining a dazzling light, the shining expanded in an instant, and 30 classmates, including me, were laying on top of a place we didn’t recognize.

A college student, accidentally reborn into the world of Naruto, becomes a member of Uchiha who is destined to be exterminated.

In this cruel ninja world, in the face of endless wars and exclusion from the village, what will Uchiha Qing do?

PS: Later in the book, the protagonist will develop a system of immortal cultivation. Cultivating Immortals in the Ninja World, have you seen it?

- Description from novelbuddy