The middle brother of the Oni trio, Zekki is the most cruel and heartless beings Nube and his allies face. Although he appears like a young teenage male, he is an extremely powerful and dangerous being who takes pleasure in killing anyone who gets in his way: male or female, young or old. His greatest peculiarity is the usage of musical terms (and even a baton) to describe the carnage and destruction he creates.

Zekki comes to the human world after three years of climbing in search of the man who now possesses his brother Baki: the exorcist-teacher Nube. After easily thrashing Izuna Hazuki the Itako girl, he makes easy work of Nube, Yukime and Tamamo in order to see the hidden "power" the teacher supposedly used to seal Baki in his hand. Once he realized that Nube did not seal his brother on his own, relying instead on Minako's control from inside the oni, he decides to stay his hand no longer. The battles between the trio and Zekki grew more desperate, with Nube on the losing side despite the help of a true demon-sealing bracelet. After sacrifices made by Nube's students, Yukime and Tamamo, Nube voluntarily unsealed the oni inside his hand and was apparently consumed by Baki. He retained his human heart, however, and after defeating Zekki was revived by the mermaid Hayame.

(Source: Wikipedia)