Father's Old Enemy: Ryukotsusei is the fifty-third episode of the InuYasha anime.
- Inuyasha deals with the repercussions of his demonic transformation, and resolves that he never wants it to happen again.
- He goes to Tōtōsai to make his sword lighter, who, with the aid of Myōga, 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, Ryūkotsusei.
- Initially, Inuyasha merely had to pierce the heart of the dormant Ryūkotsusei, but Naraku appears and awakens the beast.
- Inuyasha struggles against the formidable opponent; Tōtōsai says that the only way for Inuyasha to defeat Ryūkotsusei is to use the Bakuryūha, Tessaiga's ultimate technique.
In the beginning of the episode, Ryūkotsusei lies dormant, Inuyasha's father's claw still impaling, and thus sealing him. Naraku proceeds to appear, melt the claw, unseal Ryūkotsusei, and vanish. Inuyasha assaults Ryūkotsusei with confidence until his sword is deflected, at which time Ryūkotsusei taunts him, explaining his extremely hard skin protects him.
Kagome and the others fly to the scene of the fight after having consulted with Tōtōsai, who tells them he is confronting Ryūkotsusei. A man accompanying them on the flight tells them that he must use the Backlash Wave (Bakuryūha) to defeat him.
The episode ends with Ryūkotsusei knocking Tessaiga 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 he thinks Kagome's name.