Just because it's "biological" doesn't mean it's preferred (can't think of the right term to use here lol)
Like if you were an orphan and your biological parents abandoned you for no good reason but your adopted family loved you and cared for you. You'd prefer the adoptive family not the biological.
There's probably just a chance Shihyeon preferred Shihyeon himself but it was never talked about lol
His real name could also have reminded him of bad memories so he doesn't like it. Or he doesn't wanna be called the same name as the other guy Hajun liked as well bc of jealousy (I FORGOT THE ACTUAL NAME AND I DONT WANNA SAY THE WRONG NAME..YAJUN?) But a few reasons really
I prefer Shihyeon or Candy personally
It could also be that he's used to Shihyeon, like Uno knows Candy's real name as well, not the real real name lol but he still calls him Candy rather than Shihyeon even outside of missions most likely because since it's always been like that they're used to those names
held off on reading this one till it was completed and i don't regret it at all omfgggg and i'm so excited for uno's story too
i'm just confused on why hajun never called shihyeon by his real name even after finding out?? idk maybe i missed smth