Episode 54

The Backlash Wave: Tetsusaiga's Ultimate Technique is 54th episode of the InuYasha anime.

Plot
As Inuyasha lays, knocked out by Ryukotsusei, Kagome and her friends, along with Totosai, arrive and witness the scene. Inuyasha wakes up to the sound of Kagome's voice, but he has been separated from his sword and taken his full demon form. He then fights with his bare claws, to Totosai's sorrow, because even if he wins, the Tessaiga won't become lighter for him. As Kagome is prepared to go with him to help him overcome his demon's blood's influence, he manages on his own to try to get the Tessaiga. Ryukotsusei fire two fireball at him, the first one InuYasha deals with by protecting himself with Tessaiga's sheath, the second one is diverted by Miroku's wind tunnel. InuYasha then reaches the Tessaiga, which helps him regain his normal hanyo state.

Inuyasha forces himself to use the Tessaiga, which then becomes lighter. He strikes the dragon to the heart, and marvels at how the blade now seem to belong to his hand. But Ryukotsusei isn't dead yet, barely scratched. Totosai remarks that he was a handful even for Inuyasha's father, and won't die unless torn to pieces. Inuyasha uses the wind scar against him, which he can now wield at will, but even that isn't enough. Ryukotsusei taunts him and prepare to send a monstrous ball of pure evil energy. Kagome and her friends go a little farther from the fight for their safety. The dragon launches the thing, and Inuyasha goes head on against it, cutting it hard with a "different wind scar". He just employed in battle the Backlash Wave for the first time. Ryukotsusei's energy is sent back at him tenfold, in the shape of multiple twisters that rip his body apart.

As Kagome, Shippo and Miroku congratulate him on an impressive kill, Inuyasha shows off his perfected Wind Scar, to the point that Kagome has to use the sit command to calm him down from his bragging.

Trivia

 * The is the first time the Tessaiga becomes lighter.
 * Inuyasha uses the Backlash Wave for the first time without realizing it to defeat Ryukotsusei.
 * This is the first time Inuyasha can use the wind scar whenever he wants