Seizo Kasumi is a character that's frequently mentioned in Samurai Champloo/Anime. He is the father of Fuu and serves as the plot device for the entire series. He is voiced by Doug Stone in the English Dub, and Kouji Nakata in the Japanese dub.
Seizo is a Japanese man with a ponytail and a purple-black kimono.
Seizo Kasumi seems to be an honorable man who cares for his family. He couldn't stand and watch as peasants starve and get mistreated. However, the rebellion would fail and Seizo Kasumi would be hunted by the Shogunate, forcing him to leave his family. When Fuu meets him again in the series finale, Seizo Kasumi understands Fuu's anger and asks for her forgiveness. He is also willing to accept his death by Kariya Kagetoki.
Long ago, Seizo Kasumi was a Christian samurai married an unknown woman, who gave birth to his daughter Fuu. During the Shimabara Rebellion (which was the uprising of Japanese Roman Catholics due to heavy taxes and abuses from officials), he was one of the leaders in the rebellion. The Japanese sought the help of the Dutch army which helped quelled the rebellion down, and the Shogunate sought for Seizo's death.
Fearing for his family's life, Seizo Kasumi ran away to protect his wife and children. Fuu's last memory of him was running through a field of sunflowers, which is why she refers to him as "The Sunflower Samurai" or the "Samurai who smells of sunflowers." Her necklace is a Christianity symbol, which is why Joji Titsingh recognizes it and warns Fuu to not show it to anyone.
Seizo appears in flashbacks and is mentioned indirectly in Lullabies of the Lost (Verse 2) when Fuu reveals to Jin and Mugen that the Sunflower Samurai is her father. He is finally mentioned in name in Unholy Union when Yuri confirms that the Sunflower Samurai is Seizo Kasumi.
Seizo Kasumi finally makes his real appearance in the series finale Evanescent Encounter (Part 3) when Fuu finally meets him face to face. Fuu expects to see Seizo healthy, but is shocked to see Seizo dying from an unknown disease. Fuu gets angry at her father for leaving her and her mom, who died a few years ago. Unfortunately for Fuu, Kariya Kagetoki had followed her after defeating Jin earlier in Evanescent Encounter (Part 2). It is revealed that the Shogunate learned about Fuu trying to find Seizo Kasumi, and initially sent Sara to kill them, but when Sara failed in her mission (allowing Mugen to kill her), the shogunate sent Kariya Kagetoki.
Due to samurai honor, Kariya allows Seizo to say his last thoughts to Fuu. Seizo Kasumi uses his last living moments to console Fuu, asking for forgiveness and saying he’s always thought about her and her mother before Kariya delivers the death blow by stabbing him in the chest. However, Seizo Kasumi is eventually avenged when Jin comes back and kills Kariya Kagetoki once and for all. Seizo's caretaker explains why Seizo left Fuu that she finally understands and makes peace with what happened.