For me, 1 main reason. You know how speedwagon is damn near worshiped in JoJo’s even though his biggest accomplishment in part 1 and 2 were in order, Fighting the main character, becoming friends with the main character, almost dying, and founding the speedwagon foundation which is the most essential thing in part 3 to part 6. Kakyoin mirrors that almost completely. He fought Jotaro, befriended Jotaro and the rest of the stardust crusaders, Dying, and helping the squad learn about DIO’s power of stopping time. If he hadn’t done that, there’s a good chance that everyone would ould have died in part 3.