A "Liver" working under NIJISANJI, designed by Maki Hitsuji (Shadowverse, Grimms Notes, Arknights, assorted light novels). Debiru is canonically genderless (but uses the masculine "boku" as a pronoun and is voice-acted by a woman), and frequently compared to a koala. Debiru's fans are dubbed 「契約者」 ("contractor"/"contractee".)

Official NIJISANJI profile:

異世界の悪魔。この世界の人間たちに存在を知ってもらい、力を強くするために活動を始めた。
目標は全人類を堕落させること。ホラー映画や漫画など、悪魔の勉強は欠かさない。
悪魔社会も結構厳しいらしい。

Translated profile:

A demon from another world. They have come to this world to make humans aware of their existence and to become more powerful. Their goal is to corrupt all of humanity. They never miss up an opportunity to use horror movies, comics, etc. as material for a demon's study. Suggests that demon society is particularly strict.