Manga by author Yuto saeduki

Emi Asai, a run-of-the-mill office worker, is currently living an apartment with her "Gay" older cousin, Kiichi Uno. A good-looking guy, Kiichi works nights as a bartender. Best friends since forever, they couldn't have been more different in their daily schedules, or their choice of lovers... Until one late night, when their relationship gets turned upside down!