Chapter 101 of the Jigokuraku manga.
After arriving at the Banko's Earth tanden, Shion tells Nurugai to stay back as he defends against the monsters approaching them but sees that he is well past his limits. They then hear the sound of the conch from Yuzuriha, signaling that everyone has reached their respective tandens and can begin to destroy them. Seeing as how the tanden is too high up for his sword to reach, Shion imbues Nurugai's sword with his strengthen Tao and throws it towards the tanden but unfortunately leaves a shallow cut. Zhu Jin feels that she is harmed from their attempt and controls the monsters to extract their Tao. Shion yells out to Nurugai to stay behind him until the next sound of the horn since her inability to use Tao puts her in danger. Nurugai then remembers the times Shion told her to stay back as he fights alone and how he relinquished his status as a Yamada Asaemon in front of Kiyomaru in order to become her guardian. Nurugai asks Shion if he meant what he said during the time, which he answers yes. After saying that she was happy to hear him state that, Nurugai rushes in to attack the monsters. At the same time, Nurugai remembers the reason as to why she cannot perceive Tao but manages to awaken this ability after correcting herself. She then tells Shion that she needs to use her own strength to survive and asks that he become her partner instead of a guardian. Shion agrees to this and asks that she take the lead until the next sound of the horn from Yuzuriha. Having been harmed once again by the two, Zhu Jin becomes furious and causes the Earth tanden to sprout multiple bodies of Mu Dan, much to Shion and Nurugai's shock.