On the sealed Nascent Soul are sealing runes formed by the Rule Power. Perhaps the Half-step Great Power is exceedingly adept at controlling the Rule Power, or maybe the Half-step Great Power doesn't want to waste too much Rule Power; the Rule Power sealing the Nascent Soul is just at a level sufficient to seal it.
Without external assistance, it's impossible to break the sealing Rule Power from within. However, the Rule Power constituting the seal is limited. Li Shiming observed and concluded that with a few days, he could leverage the power of the other four Nascent Souls to break the seal.
He recalled that finger from back then and thought of that indescribable might; it was a feeling akin to an ant facing a dragon, a sensation he rarely experienced after advancing to the Nascent Soul Realm.
