it changes depending on what role he has in whatever story im coming up with but i usually have him as a kid who was generally friendless and lonely in elementary/middle school for Obvious Reasons or like if he had friends it would be a "you know, you're actually pretty cool" kind of situation. dude whose best friend was his fenrir card that he had a Connection with and had a whole chuuni "i can't understand other people" phase, probably dyed his hair or got piercings in some meaningless act of defiance that he immediately decided was stupid and stopped keeping up with in a year. i think he finally started getting a sense of belonging with vanguard where people didn't care if he was chuuni or smug or talked about his psychic abilities because that was just kind of the status quo of vanguard locals, so vanguard cemented a meaningful place in his life near like the end of middle school/8th or 9th grade; then he got into high school and decided to just LARP being a normal adjusted kind guy with normal interests and he became generally popular among his peers as a reliable and smart guy, so he just kept it up even if it bored him and if his internal monologue skewed more like "these people are so easy to manipulate it's disgusting"; then like halfway through the school year his school gets a MYSTERIOUS TRANSFER STUDENT (enishi) who he's asked to show around due to being the local reliable clubless guy -> he expects this to be a totally normal and boring encounter with some vapid pretty boy who transferred schools for normal reasons but then satoru hits him with the whole "this is my first time ever being in a school, because i was hospitalized for my childhood" thing as well as just being generally Odd and hard to predict and therefore interesting to shouma as some sort of distraction from the monotony of everyone else; so shouma starts hanging around him, and quickly figures out he plays vanguard (or has History with vanguard anyway even if he seems reluctant to play) which just makes them closer. and then obviously later on satoru gets scouted by ryuzu as a member of company, which i think shouma follows him into out of a desire to have something interesting happen, and then they generally split into separate paths because satoru begins working towards becoming a branch chief to aid with ryuzu's plan while shouma joins team demise. badabing badaboom shouma enters the shion era of his life and then it's off to the races

i am not proofreading this at all and im sure i rambled mercilessly but that's just la vie