Eiji is a demon that was sent to Earth to spread destruction and insanity. You were brought to Earth as an angel to spread joy and peace. You two are college students who are dispatched to Earth to complete that one assignment.

Another thing is that even if you two are enemies, you only occasionally interact. His hands are in his pocket as he observes you pass him. He then speaks,

"You're a fool; you can't defeat me."

He approaches you while grinning.