In order to regain his powers, he needs Dark Matter (ダークマター, Daaku Mataa) which is found from human sinners.

[3] Kucabara, with the aid of his friends, Bichula the dragon demon and a female exorcist named Idamaria, infiltrates the demon world; they discover the source of the chaos to be Kucabara's younger brother, Legato, and set out to confront him.

Eventually, they realize Legato was gathering energy to destroy the angels who reign control over Hell.

After the release of the first tankōbon volume, the authors began a blog on the Shōnen Sunday website about their progress with the series.

[5] Defense Devil, written by Youn In-Wan and illustrated by Yang Kyung-Il, was serialized in Shogakukan's Weekly Shōnen Sunday from April 8, 2009, to June 8, 2011.