Mana Oath.
Mana Oath and other Oath magic is a magic similar to curses without any dark or evil mana necessary in the process. Mana Oath is one of the strongest Oath magic that existed, and one of the Oath magic that couldn't be broken once the magic Oath was made.
The Mana Oath creates invisible chains of mana created by the caster itself that enveloped the heart of the caster. Those who break the Oath will have their heart crushed by the chains created by their own mana.
Mana Oath is a magic that not all people are capable of using. The creation of the magical chains needed a considerable amount of mana and a resolute heart. A sliver of doubt or unsure about the oath wouldn't activate the Mana Oath.
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"I, Surena Ekaitza, former loyal knight of the Veilleux House, hereby swear that I will dedicate this life that had been saved by you, for you alone. By the sword on my hand, I offer you my body and soul," (Surena)
