The drawing shows the last momemts of BF before the First Chapter.

Boyfriend is devastated. He wished to do something, but he's unable to. He cries because Girlfriend got corrupted and he couldn't do anything.

This black thing is a corrupted soul. What do i mean by that? Here's an explenation :

Monster created some sort of a manipulation system. When a person is fully corrupted, before he'll go into coma he'll see a black anomally. It will make people lose the battle.

This is concept art for the Extras Volume no.2.