Upon seeing Miroku's performance, Uchiha Chi was quite surprised by her strength. Compared to Shion in the original story, the difference was like heaven and earth—she was solidly at the Kage level, specifically a Kage-level expert proficient in Sealing Techniques, and supported by a massive pool of chakra. Even if he were to face her himself, he would have to exercise the utmost caution. Of course, her combat experience was likely severely lacking, which was a very fatal flaw.
After reinforcing the seal, Miroku once again invited Uchiha Chi, hoping he would enter the interior of the seal with her to investigate. Hearing this, and combining it with the information he already knew from the original story, Uchiha Chi instantly realized that she must be hiding something, while also noticing how much she cared about whether he went or not.
Therefore, he refused Miroku on the grounds of insufficient strength, though his attitude was not very firm, intending merely to test her.
Chapter 109