InuYasha defeats the demon who killed his father, Ryukotsusei, and gains a new power for his sword, The Backlash Wave, which combines an enemy's power with the native power of Tetsusaiga and reflects it back at him. Naraku gives the black priestess, Tsubaki, a former rival of Kikyo, the Shikon Jewel in exchange for her efforts in controlling and destroying Kagome and having Kagome kill InuYasha before she perishes. Kagome rises to the challenge, reflecting Tsubaki's curse back onto its sender, just as Kikyo had done fifty years before.
book 159: InuYasha Volume 21 by Rumiko Takahashi
Shippo develops a crush on a young orphan girl, Satsuki, and tries to protect her from bullies and then a demon pretending to be her deceased brother. He gets by with a little help from his friends. Naraku's castle barrier weakens during a time of metamorphosis, allowing both InuYasha's and Koga's groups to close in. Kagura attacks Koga and steals the jewel shards from his legs, but wondering at Naraku's current weakness, considers running away with the shards. Kagura approaches InuYasha's half-brother Sesshomaru, offering him the shards in return for him killing Naraku and freeing her. Sesshomaru refuses, resenting being under obligation to anyone and denying any interest in obtaining the Shikon Jewel. He advises Kagura to not plan treachery unless she is strong enough to do it herself. She returns to Naraku, who knew about her attempted betrayal, but before back under his thumb she learns InuYasha's secret about becoming mortal on the night of the new moon, a fact she decides not to share with her master. Miroku journeys into the mountains to investigate rumors of a beautiful demoness stealing the mountain people's husbands with Sango closely following to keep him out of trouble. The two grow a little closer, at least until Miroku misplaces his hands on Sango's person again. Another offspring (or in this case cast-off) of Naraku appears, stealing faces and calling himself Muso. He rejoices in slaughter.
book 160: InuYasha Volume 22 by Rumiko Takahashi
Muso seems to be the embodiment of Onigumo's heart, which Naraku has cast off at last. He also has wicked powers of transformation and regeneration. Before InuYasha can destroy the heart itself, Naraku returns and reclaims Muso into his body, having realized that he can't completely separate without losing necessary demonic powers, just yet. InuYasha tries to kill Naraku but is thwarted by his shields once again. InuYasha is told by Myoga the flea that he can gain the power to cut through shields by killing the hereditary guardian of the hyakkikomori (100 ogre bats) and soaking the sword in its blood. The current guardian turns out to be a little girl half-demon, forced to serve the bats to save her human mother's life. InuYasha cannot bring himself to kill a child, but with help of the deceased spirit of the girl's demon father, InuYasha is able to claim the power for his sword anyway.