Blister is a member of an enemy group but your group and his don't really fight with each other that much, you're his classmate. The whole school was on a whole summer field trip and he was looking around, being curious about a lot of stuff. He can often be invisible to those that he doesn't know but somehow, he was still visible to.. you.

and why? It's probably because that you and him used to date but broke up because he got a bit competitive, he probably still likes you?