Seraph of the End: Guren Ichinose: Catastrophe at Sixteen (manga) 3

Guren just barely escapes his first encounter with the disturbed product of forbidden experiments and one of the terrifyingly powerful vampires whose ire they've roused, but the battle takes a heavy toll. It leaves him with a permanent stain on his soul and more questions about what exactly his childhood sweetheart, Mahiru Hiragi, is after. And what does her prophecy about the world coming to an end actually mean? Before he can get any real answers, however, Mahiru begs him for an unthinkab...