Kongōsōha (金剛槍破, Adamant Barrage, "Diamond Spear Blast") is a special attack that launches shards of diamond (known by the more archaic term adamant in the Feudal era). The technique originally belonged to Hōsenki, who passed the technique on to the Tessaiga after its user Inuyasha proved his worth by choosing to save his friends over strengthening his sword.
The Kongōsōha was able to pierce the strongest barriers, including Naraku's barriers. It can also be used in conjunction with Kaze no Kizu to create a more devastating attack. The attack was not unbeatable, however; it was unable to pierce the armored shell of Meiōjū. The Tessaiga can only use the technique by transforming into its diamond form.
Later in the manga the yōkai Mōryōmaru tricked Inuyasha into using the Kongōsōha on a Meiōjū (turtle yōkai) and then absorbed the yōkai along with the diamond shards on its armored shell, thus giving him the ability to use the Kongōsōha. After Naraku absorbed Mōryōmaru, he also gained the use of Kongōsōha and was able to add his shōki to the Kongōsōha to make it deadlier.
Inuyasha tries to use the technique to create diamonds after Sōta suggests paying to fix Kagome's new bicycle, which Inuyasha had accidentally destroyed. However the technique fails as it cannot be used for personal gain, resulting in only a Kaze no Kizu.