Soul Energy, Spiritual Energy, Mental Energy, and a Tangible Will at least.
Even if one had all of these four requirements, it was still not easy for an individual to create a natural Weapon Spirit.
One needed a vast amount of soul energy, spiritual energy, and mental energy to be able to form a natural weapon spirit.
If one failed to possess enough energy, the backlash would be immense and both the weapon and the individual might get destroyed as a result of this.
And for the person's Will, one had to split part of their Will to create a Natural Weapon Spirit, and splitting one's Will was an extremely painful and dangerous process.
If one was not careful when splitting their Will, they could cause irreparable damage to their Will. And even if it was done correctly, one would have to take a lot of time and resources to heal the severed part of their Will.
