Naozumi Kurosaka

Naozumi sees himself as a rival to Nagi. He wields the "Headache Octopus", a brain parasite that gives its host many powers, yet makes them suffer from chronic headaches. Due to his talents and the surgery he underwent to host the Octopus, he's a Class A assassin at "The Academy". He is introduced as an antagonist in the first arc, trying (with the help of his sister Touko) to take down Nagi.