Koichi's Penthouse is the current home of Koichi Haimawari, located in Naruhata. Koichi decided to live here because it is near the city center and how cheap his rent is.
On the exterior, is just an old penthouse that was lazily annexed on the roof of an old, beat-up building (likely unlawful construction).
The penthouse has a main room, where Koichi carries out his daily life, a kitchen and a bathroom; and has basic furniture. After the formation of Naruhata Vigilantes, there is an extra area separated by curtains, where Kazuho Haneyama can change her clothes.