怪奇幻想夢物語 怪獣綺譚 朧十夜

The nation of Itaru is shielded by four legendary beasts
representing the sky, the earth, the day and the night.
Here people are given birth as a girl with no exceptions,
and later choose to become either man or a woman.

This is a story of siblings who shoulder a fate to see the truth...

[From DLsite]