Dokuchi

Akane:

A younger, much newer demon among the ranks that latched herself to his tail. He's formed a sibling bond with her; protecting her from slayers and other demons alike as she does not have a great handle on her abilities yet.

Azumi:

Despite having a rocky start to say the least, Dokuchi was incredibly impressed by the slayer's determination and abilities in their first fight. Subsequent encounters brought her to see he was almost entirely concerned with Akane's safety, as opposed to his own growth - further speaking had them come to friendlier terms. Eventually, Dokuchi would come to side with the slayers through his hatred for Muzan and desire to find a cure for his affliction as well.