Li Yu needed Kindling Fire because refining a Sword Pellet required the assistance of spiritual fire, which could only be subdued by cultivators at or above the Foundation Establishment stage.
When a Qi Refining stage sword cultivator comprehended natal sword Qi, they could begin refining a Sword Pellet, but their cultivation level would be insufficient to subdue spiritual fire. This presented a dilemma unless they had the help of a high-level cultivator who had already subdued a spiritual fire.
Li Yu did not know any high-level cultivators who had subdued spiritual fire, and Wang Wei was too busy reading books to ever spend time subduing one.
Chapter 35