Kanojo no Kagi wo Akeru Houhou

Haruma's first impression of the new transfer student, Chitose, would be striped panties. Running into her in the hallway, Chitose's panties greet Haruma before they even know each other. Immediately, Haruma finds himself attracted to this mysterious panty girl, only to find out that she is transfering into his class AND she's going to be the new house keeper at his apartment.