Ichigo with the spirit of Zangetsu

Ichigo with the spirit of Zangetsu while wielding his zanpakuto.Ichigo zanpakuto is named Zangetsu (??, lit. moon cutter or cutting moon?). Ichigo calls him "old man" or "uncle" (????, ossan?), since Zangetsu's spirit resembles a 30-40 year-old man. Zangetsu has also been called the "black-clothed man" (????, kokui no otoko?).

When Ichigo first becomes a shinigami, his zanpakuto is simply an oversized version of a regular sealed zanpakuto, complete with an equally oversized sheath on his back. The large size is due to Ichigo's immense spiritual power, which he didn't know how to control. Byakuya Kuchiki cuts off most of the blade during his first encounter with Ichigo and Kisuke Urahara subsequently slices it down to the hilt during their training. As a result, Ichigo was forced to learn the name of his zanpakuto and release its true form.

Initial Release

The released form of Zangetsu resembles an oversized, though more elegant, cleaver. The sword is as tall as Ichigo is, 174 cm, and has a black blade with a silver edge. Ichigo's zanpakuto is always in its released state, unlike most shinigami who can seal their zanpakuto after releasing it. Yoruichi Shihouin has stated that his zanpakuto is a full-time released form type, implying that it is simply a type of zanpakuto that, once released, remains in said state. The only other person to possess such a zanpakuto is Kenpachi Zaraki. Because both men possess unusually large amounts of spiritual energy, this zanpakuto type would seem to be the result of it.

Ichigo carries his zanpakuto on his back by the cloth wrapped around the handle. When not in combat, the cloth extends to cover the rest of the sword and falls away when necessary, shrinking back to a managable size. The cloth can also be used to swing the weapon like a flail and toss it at opponents, but this rarely done. Zangetsu's special ability is the getsuga tensho (????, lit. moon sky-piercing fang?), which fires concentrated energy blasts from the tip of the blade in the shape of a crescent moon. Ichigo uses this ability without knowing its name several times, but masters the technique later on when he discovers its name. As stated by Zangetsu, knowing and not knowing the name of an attack makes a difference in the amount of power that it releases.

Source : quizilla.com