Twenty-eight-year-old Kippei switched places with 18-year-old Kippei---. Keita and Kippei have been together for ten and a half years. The two are like family, but they are both frustrated by their inability to be honest with each other. A proposal they can't make, sex they can't have without getting drunk... The day after breaking a mug of memories, Keita wakes up to find a strange boy beside him. He turns out to be 18-year-old Kippei -? The two of them try to get back together after this untrue accident, but...? 28歳の桔平が、18歳の桔平と入れ替わった―――。 付き合って10年半の圭太と桔平。家族同然の二人は、“今さら素直になれない”もどかしい思いを互いに抱えていた。 切り出せないプロポーズ、酔わずには出来ないセックス…。 思い出のマグカップを割ってしまった次の日、圭太が目を覚ますと横には見知らぬ少年が。 彼の正体はなんと18歳の桔平で――!? 嘘みたいなアクシデントに、二人は元に戻るため奔走するものの…？