Octoroo

Octoroo is a servant of Serrator and the one who nursed him back to health after the demon finally escaped from his seal at the bottom of the River of Lament, following Blackout's first destruction of Earth. Octoroo doesn't mind how his master frequently belittles him; on the contrary, he's still constantly worried about his master, stating that Serrator is still not recovered enough to enter the battlefield. Nonetheless, he's considered a valuable asset by Serrator, and is almost singlemindedly loyal to the much more powerful demon.

Biography
Little has been shown of Octoroo's personality. However, his only desire is to serve and please Serrator, and to make sure his master's health is constantly taken care of. Despite frequently being a target of Serrator's insults, Octoroo is still fiercely loyal to his master, and Serrator has plainly shown that he values Octoroo's abilities. He tends to begin statements with "ooh-ah-ooh!" and rhyme.

Abilities & Powers
Serrator has stated that Octoroo is even more knowledgeable in the arts of sorcery than himself, and is a potent brewer of unnatural mixtures. Octoroo is the one who still brews medicine that Serrator uses for pain and exhaustion, and took care of his master while Serrator recovered from his escape.

Trivia

 * Prior to Serrator's introduction, Octoroo was seen in shadow, unnamed, spying on Mayuri Kurotsuchi while the Shinigami Captain researched a ruined planet. He quickly retreated, however.