Aoharu x Machinegun.

When Hotaru moves into a new apartment alone, there's a mysterious man standing nearby the apartment. Hotaru decides to confront the man, who turns out to live in the neighboring apartment. The next day at school, Hotaru's best friend Kanae tells Hotaru that a host tricked her out of her money. When Hotaru goes to confront the host, he happens to be none other than Hotaru's neighbor, Masamune?!