The final boss of Groove On Fight, Bristol-D is Bristol Weller's true identity. Bristol-D is a dark summoner who gained huge influence worldwide and also great financial power by committing several crimes in the year 2115. When this was discovered, he was arrested and put in jail, but he eventually managed to escape. With the help of the technology present on his era and his abilities as devil summoner, Bristol-D traveled to the past, changing events to his convenience to finally conquer the world. Most of his techniques involve summoning demons to attack his enemies. He also has the ability to control other people's minds.

Kazuma Kaneko, one of the main character and demon designers of the Shin Megami Tensei series, was assigned to create a character for Groove On Fight with the idea of making a connection between both series, so it was decided that the final boss would be a demon summoner. Many of the demons that Bristol-D summons are in fact cameos of various demons from the Shin Megami Tensei series, which is also published by Atlus. Likewise, Shin Megami Tensei's Persona series has referenced Power Instinct on a couple occasions.

Some of the demons summoned by Bristol-D, include: Amon, Beelzebub, Buer, Flaurus, Gaap, Incubus, Leonard, Malphas, Nekomata, Orobas, Pixies, Succubus, and The Damned.