Tatsuta Ōtori is an ordinary high school student, initially blending into his class without distinction or interaction with prominent peers. His background is typical teenage student. This changes during routine cleaning duties when he partners with Luna Ishikawa, a vampire transfer student. He discovers her concealed secret: despite her cool and mysterious exterior, she struggles profoundly with the fundamental vampire ability of consuming blood.

Following this discovery, he proactively offers to assist Luna in overcoming her deficiency. He volunteers as her practice partner, permitting her attempts to feed on him while providing guidance to improve her technique. This training arrangement forms the basis of their dynamic. His involvement evolves beyond mere assistance, becoming consistent support as Luna works to refine her blood-sucking skills. His presence contributes to chipping away at Luna's aloof image among classmates, revealing her true, less proficient nature. Their collaborative efforts involve repeated practice sessions, each incrementally advancing Luna's abilities.

Over time, through their sustained interactions focused on her training, Luna develops romantic feelings toward him. His role transitions from ordinary classmate to trusted confidant and essential partner in Luna's personal journey to master her vampiric traits, reshaping both their daily school lives and deepened bond.