Curse Commandment (呪戒, Jukai) is mysterious technique needed to use FLS.
Curse Commandment is pattern that's planted on one's body. It is a technique which turns raw Existence into a power to use an ability. It works pretty much like normal people's arteries, carrying FLS around one's body. Voids, Autonomic Nerves, and possibly Re-Births are currently the only known beings that use a Curse Commandment.