Tonbokiri was forged by Fujiwara Masazane (藤原正真) of the Muramasa school (村正). This spear became famous for being used by the warrior and daimyou Honda Tadakatsu (本多忠勝). Tonbokiri was the last blade to join the Three Great Spears of Japan (天下三名槍 Tenka Sanmeisou), along with Otegine and Nihongou.
Tonbokiri's name has a story behind, which tells that Honda Tadakatsu left his spear aside to rest after one of his battles, and a dragonfly perched on the tip of the weapon. In that instant, the unlucky insect was cut in half, without any movement being necessary. Tonbo (蜻蛉 dragonfly), kiri (切 cut).
Tadakatsu Honda was famous for participating in numerous battles and devote his whole life to the Tokugawa family, especially to Tokugawa Ieyasu (徳川家康). Tonbokiri accompanied him on many of his sorties, and a interesting detail is that Tadakatsu adapted the size of his spear as he needed. It is said that Tonbokiri's original size was about 3.9m, but at some point, someone wrote in the sword records that it measured up to 6m. However, during Tadakatsu's last years, Tonbokiri was shortened to 90cm to remain useful until his death.
Currently, Tonbokiri belongs to a private collection and is exhibited sporadically (last chance to see it was on 2015/02/15). The last time that Tonbokiri was seen publicly, was 10 years ago, but there is a replica in the Ieyasu and Mikawa Bushi Museum that is always on exhibition.
The design of this character in Touken Ranbu is very loosely connected to the former owner of the weapon, Honda Tadakatsu. Perhaps only his strong physique and stamina are based on that warrior (Tonbokiri has a Survival of 62, the highest in the game along with Taroutachi's).
The game also includes Tadakatsu's inseparable companion, Mikuniguro (三国黒), the horse which followed him to all battles until its death at the Battle of Sekigahara. This is horse #02 in Touken Ranbu.
It is said that swords made by blacksmiths of the Muramasa school brought bad luck to the members of the Tokugawa clan. Many of Muramasa's works were used to kill the vassals and soldiers of this clan. Even Ieyasu was wounded several times with one of them. Strangely, the only weapon made by Muramasa that has been very useful for the Tokugawa family is Tonbokiri.
The marks on Tonbokiri's chest are Siddham script (bonji, 梵字). They can be read, top to bottom, as "ka", "kiriku", "sa", and are associated with Buddhist figures Jizô Bosatsu (地蔵菩薩), Amida Nyorai (阿弥陀如来) and Kanzeon Bosatsu (観世音菩薩), respectively. Each of these figures is in turn associated with a motif in Japanese Buddhism: earth, pure light, and mercy.