He transmigrates into the world of One Piece.
In the beginning, when Monkey D. Luffy invited him to board their ship, Ren joined the Straw Hat Pirates.
But because he learned his lesson along the way and kept killing the low-health enemies, he had a dispute with other members of the Straw Hat Pirates.
In anger, he quit the Straw Hat Pirates directly.
With a half-blood from the Lunarian race, he unintentionally acquired a Mythical Zoan Devil Fruit, Horse-Horse Fruit, Model: Qilin.
So Ren turned around and joined the Beasts Pirates and became Kaido's son-in-law and Yamato's fiance.
Before the Summit War, faced with Luffy's request for help, he coldly refused.
"Sorry, I don't want to play house with you anymore!"
"From now on, please call me the fourth calamity, Ren, the butcher!"
"Father-in-law, you have been on the throne of the strongest creature on land, sea, and air for too long. It's time to step down and give way to others!"
"I declare that starting today... all members of the new Beasts Pirates must be Mythical Zoan users!"