He is Wakana's father in the Tari Tari franchise.
Back in the old days, Keisuke and Mahiru married after Mahiru asked him. During their marriage, Mahiru tells Keisuke not to tell Wakana about her sickness. Mahiru did not want Wakana to be sad.
Keisuke Sakai is originally created by Evergreen and illustrated by Tomiyaki Kagisora. He first appears in Tari Tari volume ? and Tari Tari episode 1: Running and Inviting. He is voiced by Kenji Hamada.