With good reason for Yuu being all :| about them. Maybe if Shinya ever indulges Yuu in his past and the crap that they made him do when he was younger (and how he's really treated no better since he's adopted and all) it might have them form a better connection. Possibly. I feel like Shinya keeps a lot of stuff to himself (can't blame him after what he's been through), maybe only ever really connecting with Guren about it.

I'm still not 100% sure if I'll put him in MoM but after speaking with you here, maaaaybe I will consider it a little more. It can be a little daunting going in/being the only character of a fandom in game and though Shinya isn't Guren or Shinoa or someone equally as close to Yuu, that can always be improved in game.