Palace of the Dragon King

Taking the shape of a black box, it can be used to expose a gaseous substance to a person, petrifying their entire body, resulting in them being preserved alive for ten-thousand years.

Etymology
The technique is named after "Ryūgū-jō", an undersea palace of Ryūjin. It also appears in the tale of Urashima Tarō, the same tale Urashiki is based off of.

pt-br:Palácio do Rei Dragão