To ignite the Lifebound Flame within oneself, one must possess a Fire Attribute Spirit Root.
The stronger the Fire Attribute Spirit Root, the stronger the ignited Lifebound Flame will be.
Generally, one's Spirit Root is determined at birth, however, Shen Feng was very special—his Spirit Root could evolve and grow on its own.
Perhaps because of his transmigration to the Immortal Realm, his physique underwent a strange transformation.
When he first arrived in the Immortal Realm, he had no Spirit Root of any attribute, but later, Spirit Roots began to emerge, and he had not just one but all the Five Elements Spirit Roots.
Although his cultivation had dissipated, the Spirit Root would not—this was a talent within his body, also considered an attribute.
To ignite the Lifebound Flame, at the very least, one required the cultivation of the Foundation Establishment Stage.