The Sennensō berries.
The Sennensō berries (千年草の果, せんねんそうのみ, "Seed of the thousand-year-old plant") were capable of curing a yōkai of poison by eating them. It only grew on a mountainous ravine that was inhabited by many yōkai.
History[]
Jaken was stung by saimyōshō while protecting Rin. She wanted to save Jaken. He told her of the herbal farmer Jinenji may have the sennensō berries that were needed to cure him. She traveled with A-Un to visit Jinenji. When Rin arrived at Jinenji's farm, she saw that he covered himself up. His mother explained that Jinenji was going through his transformation period that made him a human, and refused to leave until he reverted. Rin explained what had happened. Jinenji warned her that the berries only grew at a ravine at the back of his farm, and that it was home to many dangerous yōkai. He promised to retrieve them when he turned back to his original self, but Rin couldn't wait for that. She decided to go alone. Jinenji drew her a picture of what the berries looked like to aid her. She left to retrieve the berries. A-Un defended her from other yōkai until she found the berries high up a cliff. She climbed up to reach them. She grabbed it, but the rock beneath her feet collapsed and she fell down the cliff calling for Sesshōmaru. She lost consciousness while she fell, then was immediately rescued by Sesshōmaru before she hit the ground. He returned to Jaken, and handed him the berries to save him.