Saihate no Ao - Ch. 4 - Disorder

[MangaDex]

 

[_Keyboard]

I think Ao and Haru were best friends. At least to Ao, Haru was his best friend. So when they hurt him (memory loss) he got angry and now kills everyone that hurt him. And that promise to meet him again is maybe the reason the monsters are targeting Haru. Maybe they are trying to kidnap him, not kill him.