Kiyomasa was born in what is now Nakamura-ku, Nagoya (situated in contemporary Aichi District, Owari Province) to Katō Kiyotada.

[4][disputed – discuss] During the war, he apparently hunted tigers for sport, using a yari (spear), and later presented the pelts to Hideyoshi.

Kiyomasa led the defense of the castle, successfully holding at bay Chinese general Yang Hao's army, which numbered 60,000.

As did a number of other daimyōs who participated in the invasion of Korea, he took a group of captive Korean potters back to his fief in Kyūshū.

[6] According to popular theory In 1598 after the death of Toyotomi Hideyoshi, the government of Japan have an accident when seven military generals consisted of Fukushima Masanori, Katō Kiyomasa, Ikeda Terumasa, Hosokawa Tadaoki, Asano Yoshinaga, Katō Yoshiaki, and Kuroda Nagamasa planned a conspiracy to kill Ishida Mitsunari.

However, Mitsunari learned of this through a report from a servant of Toyotomi Hideyori named Jiemon Kuwajima, and fled to Satake Yoshinobu's mansion together with Shima Sakon and others to hide.

[9] However, historian Watanabe Daimon stated from the primary and secondary sources text about the accident this was more of legal conflict between those generals with Mitsunari, rather than conspiracy to murder him.

[7][11] Muramatsu Shunkichi, writer of "The Surprising Colors and Desires of the Heroes of Japanese History and violent womens”, gave his assessment that the reason of Mitsunari failure in his war against Ieyasu was due to his unpopularity among the major political figures of that time.

[citation needed] Katô joined with Tokugawa and during the Sekigahara campaign (August–October 1600) fought Ishida's allies on Kyushu and took a number of Konishi's castles.

For his service, Katô was awarded the other half of Higo (formerly owned by Konishi, who was executed in the wake of Sekigahara), bringing his income to nearly 500,000 koku.

[citation needed] In his later years, Kiyomasa tried to work as a mediator for the increasingly complicated relationship between Ieyasu and Toyotomi Hideyori.

[18] William Scott Wilson describes Katō Kiyomasa thus: "He was a military man first and last, outlawing even the recitation of poetry, putting the martial arts above all else.

His precepts show the single-mindedness and Spartan attitudes of the man, [they] demonstrate emphatically that the warrior's first duty in the early 17th century was simply to 'grasp the sword and die'.