Residents of Yuragi-sou
Nakai found Yuuna with amnesia in Room 4 of the Yuragi Inn. Due to how Yuuna is bound to the room and the Inn, Nakai lets her stay and gives her name. Yuuna is very grateful for Nakai kindness and the two enjoy each other's company. When there was Career Counseling, Nakai decided to go as Yuuna's official guardian.
She assists the Oni by cleaning her room, at times when it is messy. Nakai is notably the one that Nonko tries to be at her best behavior around.
She like to feed Yaya her favorite, so they are close.
When Sagiri fist moved to the Yuragi Inn, Nakai is the only one who greets her formally. Like with the rest of the Yuragi residents, Nakai looks after Sagiri, and Sagiri respects Nakai as the caretaker of the Inn.
After being knocked out by Yuuna in the bath, Nakai attends to Kogarashi until he awakens, welcoming him to the Inn and introducing him to the other residents. She jokingly pressures the young man if he doesn't pay his expenses, he won't get any food. Overall, she has friendly relations with him and thinks of his well being. She came to Kogarashi's Career Counseling as his legal guardian.
She has known Tsutomu since he was a kid. He played with her and even asked her to be his wife when he grows up.
In the present, he is the principal of a middle school and is able to fulfill her dream of attending school just like a normal girl. It is likely implied that he has learned her true nature and notes her appearance will remain unchanged for very long time.
The Official head of the Yuragi Inn. Because the Manager is mostly absent throughout the series, Nakai takes charge in running the Inn. Nakai appears to know the Manager very well as she explains about what the Manager does, and also explains the various supernatural items the Managers collects and drops off at the Inn.