よふかしのうた

A teenage boy named Ko Yamori has stopped attending school and spends his nights wandering the streets, unable to sleep. One night, he encounters a strange girl named Nazuna Nanakusa who introduces herself as a vampire and invites him to her place. Nazuna explains that she only feeds on people she likes and offers Ko the chance to become a vampire himself if he falls in love with her. Ko, feeling a strange attraction to the freedom of the night, begins spending more time with Nazuna as they explore the city after dark. Through their nighttime adventures, Ko starts to experience a side of life he never knew during the day. (Unreviewed summary by Grok 4.1)