Akazu no Ma no Shibijin

The Toudou family is a prominent business dynasty. The head of the family, Michihiro, had a mistress named Satomi in addition to his pregnant wife, Chika. One rainy night, Michihiro and Chika got into a heated argument over this matter, and Chika committed a gruesome suicide with a knife. Her body was buried, but inside the coffin, a baby girl named Maoko was born.

(Source: Kaiki Manga no Anagura, translated)