Serina's use of magic erodes her "sense of justice" and increases her libido. She ends up masturbating at home after battle, using the youma she fights as fap material. :D
This goes badly when she encounters a horde of youma. Her magic runs out, and her body gets aroused. She's captured by the youma, and their tentacles assault her. After climaxing, her new power activates: "time leap", and is returned to the moment before she's captured. Momentatirly confused, she fights but is beaten and tentacle-raped again.
Her time-leap ability once again activates, but her lust gets the better of her and allows herself to be defeated, anticipating the pleasure she'll experience over and over. :D