It’s not George, George the second, Jonathan, Johnny, Joseph, Holly, Hplly-Kira, or Jotaro just for the fact that they’ve contributed to the family tree. I’d also like to rule out the main JoJo’s since they each actually accomplish something. I would also like to rule out YoJo for the fact he contributes to the creation of Sailor Josuke. Kei/Kyo the sister of YoJo and daughter of Holly-Kira will also be excluded for helping the journey of Sailor Josuke. That leaves The Sons of DIO and the pucci brothers on a technicality, so I will eliminate the pucci brothers due to both of their goals and actions heavily impacting their part. I will also take out Donatello for the fact he brings out heavy weather. Then I will take out Rykiel for being Apollo 11, so that leaves ungalo. Therefore Ungalo is technically the most useless Joestar, if it wasn’t for nickolas Joestar which only only contributed to the terrible relationship between Johnny and is father, which now that I think about it is more useful than ungalo. So ungalo is the winner, or loser here. Or Shizuka if we count adoptions.
