Seal of the Moon: Ice Prison was named by Sumaru who saw the technique when glancing into the Library of Decease. From what he gleaned, Sumaru speculated that this technique puts those trapped inside in a state of suspended animation. Once the Library was raided by Team Inojin, the secrets behind the technique were revealed. It actually is not an Ice Release technique but a Lunar Release. Sumaru's speculations weren't far off as the ice is actually close to the temperature of absolute zero. The inner portions of the ice are kept warm so that the victims are kept alive but only just. This technique could be used as a means of torture as the creeping ice can be perceived as "so cold it burns".