I am a firm believer that Junpei and Fushiguro would get along. Not in the same way as him and Itadori, but more of a comfortable presence sort of thing.
I’ve seen people think they wouldn’t because of their takes on morality arguing that Fushiguro wouldn’t like him because of his willingness to kill hurt those who hurt him. Junpei on the other hand being uncomfortable with Fushiguro’s bluntness and intimidating nature, but I personally disagree,
Fushiguro’s mentality is heavily dependent on his comparison to good vs bad people, where the scale itself is incredibly flawed due to Tsumiki’s influence and his idolization of her, which in turn caused an effect where he idolizes anyone who is her level of good. However he still views those type of people as annoying for their—in his opinion—willingness to let people who hurt them hurt them again(his view of forgiveness). This thought process leaves him in a position where he feels a sort-of obligation to protect them because they won’t protect themselves.
This mentality lead him down a spiral where he has no self-worth as he himself is not on a Tsumiki’s level of good, in fact in comparison he is down in the pits.
Of course that means there is layers, there is an in-between, not between good & bad, but between bad & bad and good & good.
There are bad people who will hurt others for no good reason, and bad people who will hurt others based on their own beliefs(Fushiguro).
This might seem to go against my earlier idea of Fushiguro and Junpei getting along, but Fushiguro himself is heavily hypocritical and holds himself to a higher standard, where even if someone scales to his level or even just a smidgen lower, he will still view them as better than himself. Only a smidgen though.
Junpei fits into this scale slightly(VERY slightly) lower, though with Fushiguro’s hypocrisy he would be higher… likely due to Junpei’s mentality being made based on his own victim hood and lack of interference by others.
Junpei’s mentality is a lot more self-centred. He doesn’t really care much about people around him unless they get involved with him. The only important people in Junpei’s life(prior to Itadori and Mahito) were his Mother and his bullies(somewhat his teachers too). His mother sort of being his Tsumiki, not in a morality way but instead his good person. The one person who treats him nicely. But Junpei doesn’t put things on a scale, there is no overall morality, it’s simply self-defence. He hates those who hurt him(in contrast to Fushiguro’s hate to those who hurt others) and likes those who are nice to him. A very simple mentality.
Now! Onto the actual fun part!
Fushiguro finds absolutely nothing wrong with self-defence. In fact he gets annoyed with people who don’t utilize it(good people who forgive). Junpei’s mentality does not counter that, Fushiguro’s more likely to justify it in his own head as Junpei finally fighting back, which he likes people doing.
Junpei’s self-centred mentality quite literally means should Fushiguro just treat him with respect he will have no problems with him. Junpei would probably get a comfort in knowing that Fushiguro does not disagree with his mentality, and even likes it to an extent.
I am disappointed in how short this part was in comparison to the rest.
ANYWAYS! This was just my opinion.