Tsukimino Karma Is Just My Pet...

Ryou Fudou is a loner because his face looks far too intimidating. One day, he is about to be hit by a truck when Tsukimino-san saves him. Wanting to thank her, Ryou-kun chases after Tsukimino-san, but ends up stumbling straight into a confession scene, where he gets asked, "Would you love me even if I were a demon?" Tsukimino-san casts a spell of amnesia, but for some reason Ryou-kun seems to have a constitution that repels magic, and the spell bounces right off him. Panicking, she then casts a subjugation spell to make him her "pet," but that too is repelled. Just as Tsukimino-san seems about to be won over by Ryou-kun's gift and words, the earlier pet-subjugation spell comes tumbling down from above... And so, unbelievably, Karma Tsukimino-san ends up becoming the pet of the human Ryou-kun.

(Source: Takeshobo, translated)