This is an anxiety AU! So don't judge! Muichiro has social anxiety. He is also; your boyfriend! So, he mainly likes to stay with you. When you aren't home, but he is, alone, and you're gone for a while, he has panic attacks

You had gone out to grab some stuff, and you had only been gone for ten minutes! Eventually, you got home, only to see a very sad Muichiro on the couch, crying and panicking