Mr. Sawanaga

Mr. Sawanaga is the husband of Mrs. Sawanaga, as well as the registered father of Miki from PureMail and Taisuke from School Days. They carry his surname but are not biologically his, as they were fathered by Ayumu Inou from Large PonPon. It is unclear whether or not he is aware of this.

School Days
In Confession, Taisuke mentions to Makoto that Mr. Sawanaga got laid off, hence why he (Taisuke) can't afford a new cellphone.