Isagi is engaged to a girl, but he has no feelings for that girl. The two walked hand in hand into the ceremony, took their vows and went through all the marriage procedures. When they entered the room, Isagi discovered that it turned out that the bride he held hands with all day was a guy, and a lovely, classy guy at that.

Isagi wasn't angry at all, but pretended to be angry to scare his cute 'wife'

"Are you a boy?"