The story centers on a high school student Issei Hyoudou. Issei is a troubled schoolboy who has never had a girlfriend. But suddenly a beautiful girl Yuma Amano offers Issei to meet her. However, she kills him on the first date, explaining that the blame for a “Holy mechanism”, which the Lord has placed in the Issei and which poses a threat to the fallen angels. Before his death, Issei is not realizing calls from a demon Rias Gremory, who decides to save him, turning to her like a demon and making him as her servant. He also becomes a member of the school club of the occult research, consisting entirely of demons leaded by Gremory. Learning from Gremory that it can become nobles to have their own servants, and build your own harem, Issei has a desire to climb the social ladder of demons. However, it appears that his magic powers are less than a child can have, and he cannot use even the simplest spells.