Aniki and me 3: switched hearts (2006)

Yuma, a trading company employee, is busy with work and has been drifting apart from his fiancee Yoko. His childhood friend and junior colleague Atsushi, who regards Yuma as an older brother, is gay. But Yuma doesn't know this. One day, Atsushi invites Yuma to a summer festival. Drunk, Yuma stays at Atsushi's apartment. Atsushi's gaze falls on the lower half of Yuma's body, as he sleeps defenselessly in his yukata robes. He instinctively reaches out to touch it. At that moment, Yuma senses something is wrong and wakes up. Upset to find out that Atsushi is gay, Yuma goes home. The next day, as Atsushi is apologizing to Yuma for the night before, thunder rumbles! Before he knows it, their bodies have been swapped. Atsushi, in Yuma's form, checks out the lower half of his brother, whom he admires, and is entranced on the spot. Yuma, in Atsushi's body, goes pale. The two are forced to live like this for a while...