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…？