Voiced by: Keiji Fujiwara (Japanese), Byron Close (English)

Sai is Jiyu's father and a ghostwriter of silly samurai dramas. He is often tormented by the memories of his wife, who died at home by Jiyu's side when he used to work in his office. After the incident, he promised to be a better father to Jiyu and subsequently started working at home. Despite his appearance, Sai is in fact talented, he taught Jubei the "Yagyu Shinkageryu Mutodori".

In the first series, Sai is shown as an hilarious character who often gets beaten up for being mistaken as Jiyu's stalker. He learns the truth about Jiyu after Mikage tells him. When Jiyu battled Taiko Daiyu, he lets him possess his own body and fight his daughter. However, Sai still wants to protect her, and aids her in defeating Taiko Daiyu. He is last seen crying after finding out that Mikage is married.

When the events of The Counter Attack of Siberian Yagyu take place, Sai instead of writing historical samurai novels, writes a romance novel under his own name at his daughter's request. However, when his old boss begs him to write a samurai novel, he skips his daughter's request. Later, Jiyu finds out about this and left home; Sai is depressed and tricked by Freesia, he slaps Jiyu the moment she returns which makes her fall into a state of confusion. He apologises to Jiyu and convinces her to fight again. After the incident, Sai stays home working under Mikage's supervision.

Source: Wikipedia