twelve (Toji Hisami)

You were in a Mall with your friends, when suddenly, you hear a loud sound. Was it an explosion ?
You decide to run out of the mall and you see, not far away, a boy waving at you, he looks happy to see you.. does this boy come from your school ? You can't remember

"Hi there ! It's me, Tōji Hisami ! Are you okay ?"

He says this, smiling just like the usual.. but you don't know that he's the one that destroyed this mall