Come on! O mighty spear of toil!
With his current level of cultivation, the Spear, as a supreme divine weapon personally refined by him, has been with him the longest and is the most compatible with his being. As long as they aren't as far apart as one in the Yin Land and the other in the sky, the Spear can roam freely within the Five Realms, patrolling the world on behalf of Yi Chengzi, measuring the world, spreading the coordinates of the magnetic field, and toiling across the world!
Although using the Human Realm as a springboard and supporting his spiritual strength with his eternal Pure Yang Holy Fire allows the magnetic field to expand in all directions and ultimately control the Five Realms, if Yi Chengzi could learn the coordinates of the Five Realms in advance and have a clearer and more intuitive understanding of them, he could take control much faster. After all, a fortress is always easier to breach from the inside.
