Seichirou is Yoshitaka's cousin. Seichirou was raised in a similar lifestyle as Yoshitaka, but was plummeted into poverty upon the death of Yoshitaka's parents. Upon finding Mitsuki's website, Seichirou made a financial comeback by forming a production company. Through a series of contests, he was able to take possession of Izumi momentarily.
In terms of personality, Seiichirou is also a lolicon uniform fetishist who loves peeping pictures and playing girl simulation games like Yoshitaka, but also is a crossdresser.
(Source: Wikipedia)