When Toyohisa was 14 years old in 1583 (Tensho 11), the Shimazu clan's chief vassal, Uwai Satokane, paid a visit to Sadowara Castle, which was his home.

Since his father, Shimazu Iehisa, was not present at the time, it is said that Toyohisa, who was standing in front of his genpuku, replied.

Ryuzoji Takanobu, based in Hizen Province (currently Saga and Nagasaki prefectures), and Okita, commanded by Shimazu Iehisa, clashed with the Shimazu-Arima Allied Force in 1584 (Tensho 12).

Toyohisa Shimazu, on the other hand, flatly denied, saying, "Even if you are in your homeland, if you know your father's problems, you will come to see him, but if you leave on the eve of the war, even if you are young, it will be a shame until the last generation."

He retied the sash after thanking him and promising Toyohisa, "If I can succeed today and live, my father can untie this upper belt."

In February 1586, Uwai Satokane told his father, Iehisa, that he needed a medicine called 'Sokoen' to cure the smallpox of Toyohisa's three brothers.

Toyotomi Hideyoshi invaded Kyushu in 1587 (Tensho 15), at the behest of Otomo Sorin, daimyō of Bungo Province (currently Oita Prefecture).

As a result, the Shimazu army lifted the siege of the castle, buried the corps in the forest while withdrawing, and prepared to fight.

On May 3, he landed in Busan with about 30 cavalry and 500 miscellaneous soldiers, and invaded to the gate, but the Korean King Seonjo had fled to Uiju.

In August of the same year, he was ordered to return to Japan with Akizuki Tanenaga, Mototane Takahashi, and Sagara Yorifusa.

On November 21, the same year, he stayed on Shiikijima in front of Busan on 20 ships, rescued Yoshihiro's father and son, and returned to Japan two days later.

On March 29, 1599, Tokugawa Ieyasu ordered him to return to his territory and consult with Shimazu Yoshihisa, and arrived at Sadowara.

In early June of the same year, he went to the Shonai War due to Shimazu Tadatsune's departure for the front.

He became the general of the attack on Yamada Castle with Tadamoto Niiro and Shigeho Murao, and captured it, and on April 12, 1600, the Shonai War ended with the surrender of Ijuin Tadazane.

On May 12, 1600, he left Sadowara to work in Fushimi and went to Osaka on June 5 to demand time for his return home.

Based on the information that the East Army will attack Gifu Castle, Ishida Mitsunari asks Toyohisa to defend Etonowatari.

However, it was said that Yoshihiro did not participate in the battle because he was distrustful of the Western Army who did not listen to the night attack proposed by him, but this anecdote was written in a secondary compilation called "ochko Shu"(collection of collected land), and since there are almost no articles on night attack in the historical materials of the Shimazu side, it can not be said that it is a historical fact.

Toyohisa, who became a scapegoat for Yoshihiro, rushed into the army with 13 horsemen including Gensuke Nakamura, Sadaemon Uehara, and Shodayu Toyama and died in battle.

According to Sappan Kyuki-zatsuroku (Miscellaneaous Records of old Satsuma), 'He defeated Naomasa Ii with a gun and drove off the punitive force of the East Army.

Incidentally, "Sekigahara Battle Picture Folding Screen" owned by Gifu City Museum of History depicts the figure of Toyohisa, who is in command of the horse.

It is said that Toyohisa's armor was obtained by Shimazu Hisayoshi, the head of the Nagayoshi-Shimazu family, in 1777 and stored in Tensho-ji Temple, the family temple of the Nagayoshi-Shimazu clan, and now it is kept in Shoko Shusei-kan Hall, where a copy of it is exhibited at Heki City Central Community Center.

Kumagusu Minakata was also told by Miharu Arakawa, a diplomat from Satsuma, that he was a Beautiful Boy besides Toyohisa Shimazu.