Shimazu Saburo is a friend of Jack who loves eating and spouts large amounts of information. He is a student at the Niten Ichi Ryū, the third son of Shimazu Hideo, and the younger brother of Shimazu Taro.
Jack first meets Saburo at the dining table in a hall in Niten Ichi Ryū. Saburo later gets him and Yamato into a bit of trouble with Sensei Kyuzo after expressing disbelief at some of the teacher's claims. Kyuzo then demonstrates his prowness by asking Saburo, Yamato and Jack to attack him, all three end up on the floor in a matter of moments.
He later takes part in the fighting competion between the Niten Ichi Ryū and the Yagyu Ryū.
Saburo enters the kukai contest. Then he takes an arrow for Jack when Moriko tries to shoot Jack at the burning of the Taka-no-ma. Saburo has to stay behind when everyone is leaving for Osaka Castle, due to his injuries, with Kiku looking after him.
He appears in The Ring of Fire in the market near Tamagashi Village. Meanwhile Jack is looking for loyal and trustworthy samurai who can protect the town from Akuma. They defeat Akuma and head off to the port city of Nagasaki.
In this book it is hinted he may have some romantic feelings for Kiku as he was partly going out on his trip as a way to impress Kiku's family.
During this book it is noted that Saburo gets very seasick and he grows to hate boats.
He declines Jack's offer to go with him to England due to his feelings for Kiku which Jack understands.
He is described as being on the large side with prominent eyebrows that look like large black hairy caterpillars. Also, he is known for his huge appetite, which probably resulted in his round belly.
- Kiku - In The Ring of Fire and The Way of the Dragon, it is hinted a romance may be forming between Saburo and Kiku, another samurai student who was at Niten Ichi Ryū. He declines Jack's offer to go to England because of Kiku.
- Taro - Saburo is also the little brother of Taro, who perished in the Battle of Osaka Castle. Saburo was always a little tense around Taro, as he didn't like having to live up to his brother's name, Taro being an excellent samurai student.