Demon Flowers Kuruizaki no Hana Series by Mizuki Hakase

The Oni have been searching for the 'out-of-season flowers' - children born from the union of Gods and humans. In the midst of this, an Oni called Ushitoru saves the life of one such child, Masata, and steals him from his family. Now 11 years have passed, and Ushitoru, Masata, and a young human girl have become an unusual family.

Masato and Nao are captured by demons. They take them to a big mansion, their secret base of operations, deep in the mountain. Masato confronts Gold, the head of demons' society called the 'family'. Just as Masato is about to be executed, Ushitora enters and saves him.

The Oni, who have eaten Japan's gods and now hold everyone's lives in the palm of their hands, have been searcing for the 'out of season' flowers: children born from the union of gods and humans. In the midst of this, an Oni called Ushitoru saves the life of one such child, Masata, and steals him from his family.