Episode 54

The Backlash Wave: Tetsusaiga's Ultimate Technique is the fifty-fourth episode of the InuYasha anime.

Synopsis

 * 1) After his yōkai blood has taken over him again, Inuyasha begins ferociously attacking Ryūkotsusei and manages to slash him with his claws; Inuyasha could've defeated him this way, though if he had his Tessaiga would have not become any lighter.
 * 2) Inuyasha proves that he still has control over himself and picks up the Tessaiga; soon after he notices that not only is the Tessaiga lighter, but he can use the Kaze no Kizu at will.
 * 3) Ryūkotsusei prepares to finish off Inuyasha with another energy blast, but, unbeknownst to him, Inuyasha cuts through the blast and uses the Bakuryūha, slicing Ryūkotsusei to pieces.
 * 4) Tōtōsai reveals that the Bakuryūha takes the opponent's own yōki and fires it back at them, along with the Kaze no Kizu; Tōtōsai also notes that the user must have greater yōki than the opponent or the Bakuryūha will not work.

Summary
As Inuyasha lays, knocked out by Ryūkotsusei, Kagome and her friends, along with Tōtōsai, 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 Tōtōsai'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 to Tessaiga. Desperately fighting his demon instincts, Inuyasha focuses on his sword and slowly makes his way towards it. Ryūkotsusei fires two lightning balls at him, the first one Inuyasha deals with by protecting himself with Tessaiga's sheath, the second one is just barely diverted by Miroku's Wind Tunnel. Inuyasha then reaches the Tessaiga, which helps him regain his normal hanyō state.

Inuyasha forces himself to rely on his own strength to use the Tessaiga, declaring that defeating Ryūkotsusei without the sword would have been useless. Tessaiga then reacts to this and to Inuyasha's amazement becomes lighter. He stabs the dragon to the heart, and marvels at how the blade now seems as one with him, like an extension of his own arm. But Ryūkotsusei isn't dead yet, barely scratched. Tōtōsai remarks that he was a handful even for Inuyasha's father, and won't die unless torn to pieces. Inuyasha evades several lightning balls only to be repelled by the dragon's tail when he goes for another attack. While frustrated, he then notices the Wind Scar has been summoned on its own, twisting around the sword blade. Realizing he can now use the Wind Scar at will, Inuyasha fires one off, but even that isn't enough. Ryūkotsusei taunts him and prepares to send a monstrous ball of pure evil yōki. Kagome and her friends go a little farther from the fight for their safety. The dragon launches the attack, and Inuyasha goes head on against it, and spotting a certain spot within it, cuts it hard with the Wind Scar. The stunned Tōtōsai realizes that Inuyasha has just pulled off the theoretical Backlash Wave. The Wind Scar twisting around and against Ryūkotsusei's yōki and overcoming it, the energy of both attacks are sent back at him in the shape of multiple twisters that rip his rock-hard body apart to his shock and bewilderment. The twisters eventually decapitate him and strike his head as it falls, blowing it to pieces.

As Kagome, Shippō and Miroku congratulate him on an impressive victory, Inuyasha thanks Tōtōsai, thinking the smith had done something to Tessaiga to make it better. On confirming that Inuyasha didn't really know what he was doing, Tōtōsai explains how the Backlash Wave, Tessaiga's ultimate technique, works, and that not only does the user need to find the right spot to slash, but that their will must be stronger than the opponent's yōki. The attack won't work otherwise. Inuyasha shows off his perfected Wind Scar by firing it off multiple times into the surrounding cliffs, to the point that Kagome has to use the sit command to calm him down from his bragging.