15-sai demo Ore no Yome!

A 27-year-old man is told not to worry by the 15-year-old girl that he finds out he's being married to. Later, the aforementioned 27-year-old man that was told not to worry by the 15-year-old girl that he found out he's being married to - and is now living with - finds a new girl, coincidentally also 15-years-old, declaring that she wants to live with the initial 15-year-old girl.