Iaito (居合刀 iaitō), Japanese training sword for iaido (居合道 iaïdō), the art of drawing the sword

Visit iaidothe sageo is first used to fix the saya at obi to prevent the sword from falling or being ripped off, a function historically attested to on the mounts of katana, wakizashi and tanto. So it's not just an ornament or a gadget... it's active safety on the tatami.
The official label also requires mastery at every stage. Visit keito shiseithe left hand holds the koiguchi with the sageo in the other fingers, to check the sheath before entry and salutes, a point standardized by the ZNKR.
Lastly, when examining in Japan, the AJKF requires that the sageo is properly tied, a sign of safety and impeccable handling.
Depending on the school, the sageo no sabaki varies, but the idea has remained the same since the Edo period, XVIIᵉ century, when it already ensured the restraint of the saya and, according to tradition, could be used to hinder.

According to tradition, the young samurai Hayashizaki Jinsuke Minamoto no Shigenobu (1542-1621) prayed and meditated for a hundred days at the Hayashizaki Myōjin shrine to avenge his murdered father. At the end of this retreat, he is said to have received in a dream the lightning technique that enabled him to draw and strike in a single gesture: the ancestor of iaido.
This "instant sword" revolutionized the art of kenjutsu, placing the emphasis on presence of mind (居) and immediate harmony (合). The term iaidō wasn't formalized until 1932, however, when the spiritual emphasis of the dō (道) took precedence over mere warrior technique; iaido has since been referred to as "Zen in motion".