This is a common plot device used to explain why a character who is "virtuous" would act against their established morals. It allows for a slow "corruption" arc that many readers of this niche find compelling.
The Hero departs for a critical battle against the Demon Lord. He leaves his Angel companion behind in a neutral town or church, believing her to be safe. The Antagonist (S...) approaches her not as a monster, but as a helper—offering shelter, information about the Hero’s mission, or a "cure" for a curse. NTR Tenshi Itoshi no Yuusha-sama ni Naisho de S...
Scenes alternate sharply between the bright, heroic battlefields or royal courts where the Hero fights, and the dimly lit, hidden spaces where the secret betrayals take place. This is a common plot device used to