THE VENGEANCE OF LEAH~ A GIRL WHO LOST EVERYTHING'S VOW TO A REAPER

"Do you swear on revenge?" A room covered in blood. My mother's lying corpse. Being helpless, I was at the mercy of the man in front of me, fully clothed in black. On the outskirts of a small town, a girl named Leah lived together with her mother. One day, her mother who was her only family, is killed by a beast controlled by an unknown being. While trying to avenge her mother, she is defeated and in danger of death. At that moment, something reached out to her... A girl who swore on revenge and an inhuman being who looks of a boy's story about love and revenge begins. (Source: MangaPlaza) — Description from AniList community (anilist.co).