Inuyasha finds out from Totosai that the only way for the Tetsusaiga to get lighter is for him to surpass his father in power. To do so, Inuyasha heads out to find Ryukotsusei, a dragon-like demon that his father was able to seal away, but only into dormancy.

All Inuyasha needs to do is stab the heart of the sleeping demon and his legacy-sword should get lighter. But when Naraku awakens Ryukotsusei, things start to look much more difficult…