Hero Syndrome, Vol. 1 (light novel) — Rei Ayatsuki

THERE ARE TWO SIDES TO EVERY STORYInfected by a mysterious being called the Goddess and transformed into unthinking creatures of havoc and slaughter, abominations known as “heroes” wage an endless war of blind justice on monsters… never realizing that these monsters are actually fellow humans. Only Charon, an elite unit led by a young man named Azuma, stands a chance against these terrifying heroes. So what might happen when Kaguya, a headstrong young scientist, joins Charon's ranks and wants to save the heroes rather than defeat them…?