Mr. 2 Bon Kurei, is a former officer agent of Baroque Works and an okama. While he was once an enemy of Luffy’s as a member of Baroque Works, the two became quick friends, leading Bon Kurei to sacrifice himself for Luffy both at Alabasta and later at Impel Down.
He is currently in Impel Down not as a prisoner but as Okama Queen in level 5.5 . There is a high possibility of him joining Luffy in future.
Momonosuke has similarities to Luffy such as being strong willed and having the ability to hear the Voices of All Things. He has the ability to communicate with the giant elephant Zunisha, being capable of seeing through its eyes and giving it orders.
Also his father Kozuki Oden left Wano to sail as a pirate and he has his father as a role model, plus Luffy has clear similarities to Gol D. Roger, and Oden sailed with Roger.
Momonosuke has potential as a fighter as well, with his Dragon Zoan devil fruit (even if it’s fake, it’s made by Vegapunk himself, and we still haven’t seen its potential).
To wrap it up, Momonosuke could join the crew after Wano as an apprentice and sail to the end of the story with the Straw Hat Pirates. There are similarities between him and his father, Luffy and Roger, and most importantly between those two pairs, supporting the idea that a similar path might be taken by Oda, showing Luffy mentoring Momonosuke, which is also a great growth experience for Luffy.
Caesar Clown is a former colleague of Vegapunk and the leading expert on chemical weapons of mass destruction.
Caesar’s dream is to surpass Vegapunk and become the greatest scientist in the world. Luffy’s crew at the moment doesn’t have a scientist it would make sense if Caesar became the Straw Hat scientist.
Caesar is hated by most of the Straw Hats, even more now that Wano Arc revealed that it was for the reason that 90% of the SMILEs eaters who ended up smiling for the rest of their lives that Doflamingo, Caesar, and Kaido named the fruit SMILE, cruelly mocking their misfortune.
As we know the Straw Hat Pirates crew is basically a family and they don’t want some murderous child kidnapper and child abuser in their family.
Caesar is evil and he doesn’t want to be redeemed.
Yamato is the daughter of Kaido. She is otherwise widely referred to as his son due to often presenting herself as a man as a result of her profound admiration for the legendary samurai Kozuki Oden and her aspiration to emulate him.
Yamato had met Ace at some point in the past. She had tried to sail out of Wano with him, but her father’s handcuffs kept her prisoner on Onigashima. After failing to set sail with Ace, Yamato had been waiting for his brother, Monkey D. Luffy, to arrive at Onigashima. For this reason, she chased and clashed with Luffy, ignoring his time constraints in order to talk to him, even if for just five minutes. She trusted Luffy enough to request his help in achieving Oden’s dream of opening Wano’s borders. Yamato wished to be saved from her father and intends to leave Wano with Luffy’s crew as a means to be free and explore the sea like Oden did.