Koi to Byounetsu

Overview

The society has changed just as the times it lives in. Now that life-expectancy had dropped to somewhere around forty years families are only allowed to raise one child. If they have more, the parents must make a hard choice and hand one over to the church which offers them for adoption to childless couples. And thus the word "sibling" was eventually lost. But perhaps some of those separated children will find their ways to one another.

Source: AniList