Kaoru is the older brother of Kanao :)
Kaoru is Kanao's older brother. Kaoru is twisted because he was triumphant that he had their father's attention. I suspect that Kaoru likes to steal attention away from Kanao.
So Sei, being the mental patient he is, contacted Kaoru to get Kanno to stalk Kaoru. Kaoru will allow himself to be stalked. This takes away Kanao's audience... so Sei has Kanao all to himself.
Sei knows that Kanao was working with Kanno. Sei doesn't want anyone to be closer to Kanao than he is.
(The even deeper twist here is that Sei finds out/knows that Kanao has a twisted relationship with his brother and uses it to his advantage.)
can someone pls explain the last scene with the message, who is Kaoru again?
Σ( ￣□￣||)