Episode 53

Father's Old Enemy Ryukotsushi is 53rd episode InuYasha deals with the repercussions of his demonic transformation. He goes to Totosai to make his sword lighter, who, with the aid of Myoga, tells him that he has to surpass his father in strength. To do this he must fight and defeat the one demon his father could not, Ryukotsusei.

Fighting Ryukotsusei
In the beginning of the fight, Ryukotsusei lies dormant, InuYasha's father's claw still impaling, and thus sealing him. Naraku proceeds to appear, melt the claw, unseal Ryukotsusei, and vanish. InuYasha assaults Ryukotsusei with confidence, until his sword is deflected, at which time Ryukotsusei taunts him, explaining his immunities.

It cuts to a flying scene of Kagome and others flying to the scene of the fight after having consulted with Totosai who tells them that he is confronting Ryukotsusei. A man accompanying them on the flight tells them that he must use the Backlash Wave (Bakuryuuha) to defeat him.

Cliffhanger
The episode ends with Ryukotsusei knocking Tetsusaiga from Inuyasha's hands and wounding him, causing his demon blood to take over, as the others fly into view, with Kagome shouting his name. InuYasha's eyes open, red in color, as you can hear him think her name.