Kousetsu's first owner, Itabeoka Kousetsusai, was a pacifist and a devout Shingon Buddhist, which explains his garb and his disdain towards fighting.
Itabeoka Kousetsusai was a retainer of Houjou Ujimasa and then of Toyotomi Hideyoshi after the former's defeat at the Siege of Odawara. Kousetsu was presented to Toyotomi as a gift, and then, after Toyotomi's death, went on to serve Tokugawa Ieyasu.
The sword that Tokugawa Yorinobu carried with him during the Siege of Osaka is Kousetsu.
Later, Kousetsu was presented to the Kishuu branch of the Tokugawa family.
Designated as a National Treasure at 1932, and redesignated as part of the new National Treasures at 1951.
Despite stating that he doesn't like fighting, almost ironically, his in-game status is among the top; at maxed Toku, his Impact stat is third after Oodenta Mitsuyo and Shokudaikiri Mitsutada, Impulse shares first place with Ichigo Hitofuri, and his total stats are second place out of all Tachis.
He is often portrayed to be a flower enthusiast of some sort, in relation to his Internal Affair costume.
He is the 'Ice' part of another name for the Rarity-4 Tachis: Ice Royal Milk Tea. Sometimes also referred to as the Queen of said quartet.