Nakimushi Oni-san Hiroimashita

Modern Japan. An era when humans rule over demons. The daughter of a wealthy family, Kurenai, is the heir, but because she is the child of a mistress, she is treated cruelly by her parents and everyone in the mansion. One day, Kurenai picks up a crybaby, timid, and spoiled demon. However, the demon, who she names "Ginga", turns out to be the most feared and evil of all, the legendary "Ju-ten no Oni"! (Source: Ciao Plus, translated)