You play as Kazuha, who must make choices that increase the other characters' affection for her as well as advance the story toward two potential endings: Merry Bad and Good. The route Kazuha ends up on is determined soon after the Prologue, and all choices after that determine the ending.
After clearing a route, the History option on the main menu allows you to restart it from any chapter, with any Almighty level (determined through choices in battle) or affection level (determined through conversation choices). This is particularly useful when attempting to achieve alternate endings.
For spoiler-free guides on how to access a character's route and both of their endings (which is necessary in order to obtain all CGs), see their pages:
Astrum: A resolute leader of an Angel guild and holder of one of the Divine Swords.
Demento: A "Fallen" who comes into conflict with Kazuha. His route branches off from Astrum's.
Radius: A Demon who prefers to clear quests on his own. He also happens to be a holder of one of the Divine Swords.
Zain: An NPC who acts with suspiciously human behavior. He belongs to neither side.
Libera: A feminine Demon who prefers to sit back and let others fight.
Hiroya: The childhood friend of Kazuha, a Demon who aids in her search for Shiki.
Poyo-Poyo: An intel monster affiliated with neither side. Unlocked only after clearing Astrum, Libera, and Hiroya's routes.
