Bankai(卍解, Final Release, or Complete Release) is the final and complete form of the Zanpakutō, it is the culmination of his communication training for the Shinigami.
Achieving Bankai is rare and even once obtained, it takes another ten years and a minimum of training to perfect its mastery. The potency of a Bankaifrom a Zanpakutō varies from one to the other and from the Special, but can be five to ten times higher than that of the Shikai Celle. Only the most powerful Shinigami can use it, it is the ultimate technique in Zanjutsu.
Bankai: Tensa Zangetsu (天鎖斬月, Celestial Chain, Sharp Moon): After Kisuke Urahara's accelerated and dangerous process of obtaining Bankaiin 3 days, Ichigomanaged to unlock his sword's second release. Taking the form of a black katana, this Bankaigreatly increases Ichigo'sspeed while increasing the power of the already great sword.
Where other Zanpakutōs increase the power of their swords or bring other techniques, Tensa Zangetsu just brings a speed boost as well as the full release of Ichigo'sspiritual power significant to the Bankai.
Getsuga Tenshō: Technique similar to that of Shikai, this Getsuga Tenshō takes the form of a black torrent with a red halo which is the materialization of Ichigo's power in Bankai. He can deploy a much greater power than in Shikai.
Ichigo Ultimate Bankai: In order to defeat Aizen, Ichigotrains in the Dangai (between worlds) for 3 months which corresponds to 1 hour in the Real World in order to learn the ultimate technique of his Zanpakutō , the Ultimate Getsuga Tenshō
Getsuga Jūjishō (月牙十字衝, Moon Fang Cross-Piercing Heavens): An advanced attack from the Getsuga Tenshō that consists of firing two of these attacks in a cross. This technique is powerful enough to neutralize Candice Catnipp's Electrocution and completely sever her arm.