From Futekiya:

Shinosuke is worked to the bone at his job at Kusonoya Hotel.

After one tiring night, he stumbles into a stranger's apartment, thinking it was his own. When he awakes, he finds himself in the same bed with the stranger -the apartment's true resident- who speaks in a foreign language.

Embarrassed, Shinosuke apologizes and tries to leave. The flustered Shinosuke sparks the stranger's interest, and the two end up having sex. Determined to leave it as a one-time thing, Shinosuke goes to work only to find that an overseas company buys the company he works at. And worse, the new general manager turns out to be Noah Shizuka Ishii, the stranger he just slept with.