After transforming himself into an adamantine staff, Enma clones himself, then boxes the enemy into a lattice. The prison wall has incredible toughness, and is impossible to break. When used for defence the enemy has no way of attacking.
Vajra is a mythical substance that can cut any substance, but cannot be cut itself. In Japanese, the term is also synonymous with adamantine and diamond, while in other contexts, it is known as the thunderbolt of the Hindu Vedic deity, Indra.