Katsunari tendency to change his allegiance quite often has garnered him a nickname Rin kai fuki (倫魁不羈), which etymologically means "too awesome to serve (only) one lord".

[3] Katsunari's tales of journeys during his life and for his friendship with the legendary Rōnin Miyamoto Musashi has produced many anecdotes about him.

[6] when he followed Tadashige to attack Takatenjin Castle in Totomi, but due to Katsuyori Takeda 's retreat, the battle did not take place.

[9][10] Yuki city historical record wrote that following the capture of Tenjin Castle, Katsunari personally received a letter of commendation from Oda Nobunaga for his military exploits in this battle.

Katsunari charging his horse without pause, while being aided by Sakakibara Yasumasa and Okabe Nagamori, until the enemy forces retreated.

[17] Katsunari were tasked to assist his father and Ishikawa Kazumasa in the siege of the Hoshizaki Castle which defended by Okada Yoshiatsu.

[19] Shortly after, Katsunari moved from mount Komaki, to Obata Castle, where he and his father rendezvous with Sakai Tadatsugu, Sakakibara Yasumasa, Osuga Yasutaka, Honda Yasushige, and others to strike Toyotomi Hidetsugu army.

[23] Later, Katsunari took action in ambushing the camp of Toyotomi general named Shirae Narisada who did not expect the attack, and personally presented many heads of the enemy he slain to Ieyasu.

[20][28] Later, Katsunari followed the Tokugawa operations in Kuwana, Mie, in Ise Province, against Nobuo Oda who now making peace with Toyotomi Hideyoshi.

Tadashige, who has lost his patience in dealing with his son's unruly behavior, immediately disown and disinherit Katsunari from the Mizuno clan.

[31] In 1587, Katsunari changed entered the service under a daimyo of Higo Province, Sassa Narimasa, where he awarded a control of domain with 1,000 koku.

[32] It was said that in during this operation to save Kumamoto castle, Katsunari once competing in military merit with Awa Narutonosuke, one of Narimasa's most famous vassal who are listed in the later era period as member of semi-mythical legendary warriors group known as "Ten Braves of Amago".

[33][34] During his time serving Narimasa, Katsunari also accepted Ibara Tomomasa, a former Ii Naomasa vassal who also run away from his lord due to troubles, into his rank.

[45] On April 22 of the same year, Katsunari's younger sister, Kanahime (later known as Seijoin), became Ieyasu's adopted daughter and married to Katō Kiyomasa.

[citation needed] Katsunari, who became the head of the Mizuno family, returned to Kariya castle due to the cancellation of the Aizu conquest and went to the Battle of Sekigahara.

[53][54][55] After he beat the Shimazu forces, Katsunari returned to Ieyasu to ask permission to participate on the Sekigahara main battle which planned in the next day.

[59] Katsunari entered Ogaki castle and immediately wrote a letter to Ii Naomasa to give pardon to Tanenaga, which accepted by Ieyasu.

Katsunari immediately execute Yahachiro to avenge his father who has been murdered by Shigemochi,[61] This caused the extinction of the Kaganoi clan.

On May 4, Katsunari was called by Shogun Tokugawa Hidetada and went to Fushimi, where he received an award of 50 gold pieces for his efforts in preventing the enemy from attack city Nara.

Later, Katsunari taking his army of 3,800 soldiers south through the night, and on the May 5, He set out with Hori Naoyori, Matsukura Shigemasa, Bessho Magojiro, Okuda Tadatsugu, Niwa Ujinobu, Nakayama Terumori, Murase Shigeharu, and others, and arrived at Kokubu at 4 p.m. to camp.

As he pursue further, he met up with the rear guard of the Toyotomi army, led by Sanada Yukimura, Mōri Katsunaga, Akashi Takenori, and Ōno Harunaga.

In the final engagement against the Toyotomi forces on the Battle of Tennōji, when Yukimura lost his momentum of suicidal charge in an attempt to kill Ieyasu, Katsunari attacked Sanada's troop with about 600 men from the west of Shoai-in Temple.

[80] Furthermore, Katsunari learned Kannabe Castle has been captured in battles three times historically, which also became his reason to relocate the center of the domain to Mount.

[82] The reason of this castle being built was Katsunari were expected to become a bulwark on the Sanyōdō highway against possible rebellion by the powerful tozama daimyō of western Japan, such as the Mōri clan.

[88] In 1626, Mizuno Katsunari accompanied the third Shogun, Iemitsu, to Kyoto, and was promoted to the fourth rank and was granted an additional 1,000 koku of land in Atsugi Village, Aiko district, Sagami Province.

[92] After the rebellion in Shimabara was pacified, Katsunari was then retired from the Mizuno clan's position to his successor, and decided to focus his works on the land reclamation project which suspended before the war.

Since Katsunari's construction of the castle town of Fukuyama, the domain's development and reclamation had consistently covered all costs, reducing the burden on farmers and townspeople, and giving land to settlers free of charge.

[94] Being violent and murderous during his youth, Katsunari were compared to his friend, the legendary swordsmen Miyamoto Musashi, in term of temperament.

[99] An eccentric figure with colorful personality, Mizuno Katsunari also hosted Kabuki troupe in Kyoto at 1608, and taking one of the performer as concubine.

[102] In modern time, the Dō (armour) set of Mizuno Katsunari were preserved in Kariya city history museum.