Gekkou Nanase

He is Takeshi's younger brother and also among those people who are insanely obsessed with Isoshima, So obsessed that when he learned about Takeshi's relationship with her, he became very mad and engaged him in a fight where he got caught in an unexpected accident that led him to despise Takeshi to the point of wanting to kill him.

He later on enrolls in the same school Takeshi transferred to.

(Source: Anilinkz)