Karasu is calm and collected, not getting rattled by his opponents. He is quiet, not speaking often. He is polite, speaking formally when addressing others. He noticeably dislikes opponents who are cowardly, instead preferring opponents who are brave enough to face him. He also seems to dislike opponents who are weaker than him, prefering to face opponents who possess either the same level of skill as him or are a bit stronger than him.
Karasu comes off as being very dark. When he had first met Kurama, he told him that Kurama is very beautiful (while stroking Kurama's hair) but is fragile, as he views humans that way. He admits that Kurama makes him happy but then states that he enjoys being blue so whenever he encounters someone who makes him happy he has to kill them. Karasu claims to enjoy the relationship between victim and murderer, stating that before the murderer kills their victim the two share a level of intimacy which is too deep for words. He also views love as a sadomasochistic relationship, believing that lovers care deeply for each other and yet hurt each other whenever they are together.
In spite of his calm attitude, a trait shared with Bui, Karasu had a deep hatred for the Toguro Brothers, who had defeated him in a fight several years prior to the Dark Tournament. Upon defeating him, they made him into their slave and told him that he will belong to them until he becomes strong enough to defeat them in battle. Elder Toguro notes that Karasu joined Team Toguro in the hopes that after they win the tournament he can settle the score with the demonic brothers.
Karasu and Bui were partners in the past, having fought many battles together. Bui was defeated and enslaved by the Toguro Brothers the same day as Karasu. Karasu and Bui have a different relationship from the Toguro Brothers. Unlike the Toguro Brothers, who are very close, Karasu and Bui seem detatched from each other. Karasu and Bui respect each other but when Karasu died at Kurama's hands Bui did not shed a tear. It can be assumed that if Bui had died first Karasu would not shed a tear for him.