Kuro-Senpai To Kuroyashiki No Yami Ni Mayowanai

This manga is based on the horror-style exploration/ero-game of the same name. Reiichi heads off for a part-time job interview, hoping to get money for a new bike, and his self-styled servant Kuro-senpai tags along. The "interview" is in a western-style mansion, but no one seems to be around. The two of them end up locked in the mansion and must find their way out.