had a guild around the time he was openly an s class and went by owen no? and then after that his brother died which is why they resurfaced as onaip. but then the way that they explained it in chapter 29 it seems that he secretly changed his class DURING his academy days as a class misclassification - but yet underaged espers aren't allowed to join a guild till they graduate from the academy right so what reason would he have to do that during his school days if he presumably didn't create the guild yet? or did he run a guild during his academy days and during the time he went to school was when his brother also died so that's why he changed his class to c class during the time he was at the academy?
I decided to reread this from the beginning again and in ch 29, adante mentions that underaged espers who want to join a guild have to graduate from the academy first. but apparently (from my understanding) he also