Time traveling into the world of pirates, Ren initially accepted an invitation to join Pirate King Luffy's crew, the Straw Hat Pirates. However, tensions arose as he consistently delivered finishing blows to weakened enemies during their journey. This disagreement led to a heated dispute with his fellow crewmates, eventually resulting in Ren's abrupt departure from the Straw Hat Pirates. As a half-blooded Lunarian, Ren unexpectedly gained the ability to transform into various creatures, including the mythical Cow Fruit, Phantom Beast Species, and Kirin Form. Seizing this opportunity, Ren made a pivotal decision to align himself with the Beasts Pirates, ultimately becoming Kaido of the Beasts' son-in-law and Yamato's betrothed. As the Summit War loomed on the horizon, Ren faced Luffy's plea for assistance with a cold and resolute refusal, declaring, "I'm sorry, but I no longer wish to engage in this charade with you!"