The word tachi itself is derived as the stem or noun form of verb tatsu (断つ, "to cut off").

Until the middle of the Kamakura period, high-ranking samurai mainly fought on horseback with yumi (bows), but as group battles by foot soldiers increased from the late Kamakura period, the importance of weapons possessed by those who did not have horses and did not have sufficient training in bows increased.

The Kamakura period was the first time that samurai ruled Japan, and powerful men were valued, and those who wanted to show off the honor of being a warrior preferred to use ōdachi.

[9] However, infantry units gradually came to be equipped with yari (spears) in addition to naginata, and because ōdachi was disadvantageous for mountain battles and surprise attacks, and only a few powerful men could use it effectively, this trend ended for a short time.

[10] Even so, sengoku-daimyo in the Sengoku period dared to equip their own troops with ōdachi in order to show off their strength and bravery.

The Asakura clan made a troop called Rikishizei (力士勢) equip with an ōdachi with a blade length of 5 shaku (approx.

[12] In the peaceful Edo period, ōdachi was no longer regarded as a practical weapon and came to be recognized only as an offering to the kami of Shinto shrines.

Ōdachi are difficult to produce because their length makes traditional heat treatment more complicated: The longer a blade is, the more difficult (and expensive) it is to heat the whole blade to a homogeneous temperature, both for annealing and to reach the hardening temperature.

As battlefield weapons, ōdachi were too long for samurai to carry on their waists like normal swords.

The Kōden Enshin-ryū taught by Fumon Tanaka use a special drawing technique for "short" ōdachi allowing it to be carried on the waist.

Alternatively, it could be used as a cavalry-on-cavalry weapon comparable to the Chinese zhanmadao, with the long reach, increased weight and slashing area of the blade offering some advantages over spears, lances, and smaller swords.

[3] It was forged by the Japanese master bladesmith Norimitsu Osafune in the former Bishū province in August 1446.