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Toshimasu was born in the village of Arako (present-day Nakagawa-ku, Nagoya), Toshimasu was born to the Takigawa Clan, originally the son of Takigawa Kazumasu. He was adopted by Maeda Toshihisa, the older brother of Maeda Toshiie. Toshimasu served under Oda Nobunaga along with his uncle. Toshimasu was originally intended to inherit Maeda family headship; however, after Oda Nobunaga replaced Toshihisa with Toshiie as Maeda family head, he lost this position. Perhaps because of this loss of inheritance, Toshimasu is well known for quarreling with his uncle.
In 1581, Toshimasu was under the command of his uncle, and made a reputation for himself through conflicts within Noto Province and was rewarded with 5,000 koku. During the Battle of Komaki-Nagakute three years later, Toshimasu went to Sassa Narimasa's rescue when he was attacked at Suemori Castle. While in Kyoto, Toshimasu met and befriended Naoe Kanetsugu, Uesugi Kagekatsu's karō. The two became close friends, and Toshimasu agreed to join Kanetsugu in the Uesugi clan's invasion of Aizu. The invasion failed, and Keiji was appointed to lead the rear guard during the retreat. Riding his horse Matsukaze into battle and brandishing a two-pronged spear, he made a splendid show of force. Due in part to Toshimasu's actions, the Uesugi forces were able to retreat largely intact.
After this, Toshimasu returned to the capital and devoted himself to arts and literature. Keiji was barred from Toyotomi’s Kyushu campaign for his wild ways. When the Tokugawa challenged the Uesugi in 1600, he once again fought with Uesugi’s army. In the battle against the Mogami, legend says he broke through the enemy lines with only eight riders, and shattered their formation. After the Uesugi clan's move to the Yonezawa Domain, Toshimasu remained as a retainer.
Keiji's armor can still be seen today at the Miyasaka Museum.
Matsukaze ("wind in the pines") was Toshimasu's famous mount. According to the legend, he was bred of only the finest horses, but he refused to let anyone ride him and eventually ran away. Toshimasu managed to tame the wild horse, possibly due to Toshimasu's own wild personality. Since then, the two were never seen apart.
Matsukaze was said to be a horse of immense strength, able to carry his master's large frame for days. Supposedly, Matsukaze ran away after his master's death, never seen again.
Depictions in fiction
Toshimasu is a playable character from the Western Army in the original Kessen and in the Samurai Warriors, Warriors Orochi under the name Keiji, and Sengoku BASARA series, as "Meiji Damaged". He is a playable character in Pokémon Conquest (Pokémon + Nobunaga's Ambition in Japan), with his partner Pokémon being Bastiodon and Terrakion.