Mareido ~Choukyou no Yakata~

Demons and humans coexist in this world. There is a legend that bloody red moon shall rise when there is a big change in the world. Main character is a human who lives with his new wife at the mansion. One day he gets ordered by his wife to train a girl brought to the mansion. During intense training the two people discover that they share something that is missing in their hearts. Can love arise during such relations? And then crimson red moon rises covering the whole sky.

[From vndbreview]