From Storm in Heaven:

They'd been drunk. More specifically, his boss had been drunk. So when Sakamoto jumped him, Kurahashi just went along with it. After all, it was just the alcohol, right? Wrong. At least, that's what his boss thinks, and said boss doesn't have a problem with trying out a relationship with a colleague he thinks is in love with him. Unable to gainsay him, Kurahashi gets dragged into a relationship he never asked for - and he finds himself getting deeper than he ever imagined.