Call of the Night, Vol. 6 by Kotoyama

[Viz] Antisocial, dorky boy seeks fun-loving, sexy vampire for blood-sucking and transforming into her minion. One sleepless night, Ko slips out to walk the streets. Life after dark is a revelation! Especially when he meets flirtatious Nazuna. Except that she’s a vampire. That’s okay. He wants to become a creature of the night too. But transformation doesn’t come that easily... Although Ko happily goes on a sightseeing trip to Tokyo with Nazuna, he tries to warn his childhood friend Mahiru about the dangers of dating vampire Kiku. And that’s before Ko learns a disturbing secret about her! Meanwhile, Detective Anko pursues one of Nazuna’s vampire friends with some stabby extralegal justice in mind. To prevent Anko from exploiting their weaknesses, the gaggle of vampire women must delve deep into their pasts. Unfortunately, Nazuna can’t remember anything from her human life! Will a decades-old appointment card be the clue to finding out who “turned” Nazuna...and why?