At the instant of the slash, the Zanpakutō absorbs and condenses Ichigo's or Isshin's Reiatsu before releasing it at the tip of the blade, magnifying the slash attack, which flies forward. This slash takes the shape of a crescent moon or wave. Ichigo uses this ability without knowing its name several times, but later masters the technique during his Bankai training. As stated by Zangetsu, knowing the name of an attack heightens its power compared to its strength when the wielder does not know its name. The Getsuga Tenshō is a powerful technique with great force, creating large-scale damage and destruction. Ichigo has used this technique in several different manners, such as striking the ground to create an omnidirectional blast to knock away incoming attacks or slashing at the ground to upturn it and crush everything in its path. Isshin's use of Getsuga Tenshō against Aizen in his Second Fusion form demolished a large radius of the Fake Karakura Town, left behind a huge crater, and was powerful enough to create a large gash in Aizen's head, prompting Aizen to call it a "splendid strike" and an attack he "fully understood".
After Ichigo regains his Shinigami powers for the second time, his Getsuga Tenshō is noticeably larger and more powerful in its Shikai form than it was before he lost his powers. A single strike from it can disperse an entire rainstorm and slice off the top of a mansion. After gaining the true form of his Zangetsu, Ichigo can fire a Getsuga Tenshō with his smaller sword simply by pointing it at his target and making a small swipe. He can also fire a black Getsuga Tenshō with his larger sword; this version is powerful enough to blast a large hole in the Soul King Palace and knock someone as powerful as Yhwach several meters back.
Enhanced Getsuga Tenshō: Tensa Zangetsu retains the use of Getsuga Tenshō, which can be used in the same manners, but in an enhanced form. When used in Bankai, these potent blasts are black with a red outline, can have their path controlled, and possess explosively augmented power and speed. During his fight with Ichigo, 6th Division Captain Byakuya Kuchiki refers to this attack as a "Kuroi Getsuga" (黒月牙, Black Moon Fang), referring to the attack's darkened color. Ichigo has stated this is originally Zangetsu's technique, which has been proven, as Ichigo had no knowledge of it during his fight with Byakuya and Zangetsu stated Ichigo was copying him when he used the technique. Ichigo can keep a Getsuga Tenshō within Tensa Zangetsu to augment his sword swings. After reforging his Zanpakutō, Tensa Zangetsu's Getsuga Tenshō becomes powerful enough to bifurcate a Soul King-empowered Yhwach, and would have killed him were it not for The Almighty allowing Yhwach to reverse his own death.
Combined Gran Rey Cero-Getsuga Tenshō: By using the longer sword of Zangetsu as a substitute second horn and with his blood as a catalyst, Ichigo can fire a Gran Rey Cero; moreover, he can combine it with a Getsuga Tenshō to create a massive slashing attack powerful enough to wound a Soul King-empowered Yhwach; though the latter quickly brushed it off, he noted that it was nonetheless a potent technique and proof that he had to begin taking Ichigo seriously.