Shogun is a mysterious person Takumi meets during a chatting session. He sends gore pictures relating to the New Gene incident to Takumi, the equation "fun^10xint^40=Ir2", and the phrase "Whose eyes are those eyes?" which Takumi often used. This event gives Takumi paranoia throughout the story, thinking he is a culprit behind the New Gene incident.

In reality, Shogun’s real name is Takumi Nishijou, and the character we know of as “Takumi Nishijou” is a delusion that he real-booted. When he was 10 years old, his family found out about a rare disease he was born with, which started taking effect at the age of ten, stopping him from growing or hitting puberty and soon after, rapidly ageing him physically to the point where he could no longer walk, he went bald, and was covered in wrinkles. It's Shogun's eyes who have always been watching Takumi, but whose eyes were watching Shogun as a kid is unknown.

His main goal is to get Takumi Nishijou to awaken his gigalomaniac powers so that Takumi can defeat N.O.Z.O.M.I. and Norose and destroy Noah II on his behalf, since he cannot stop them due to the limitations of his body.

He later dies after Takumi manages to destroy Noah II.

(Source: Wikipedia, Chaos;Head Wiki)