The Death Heater is a poison inside the wristbands that Tsuna's and Xanxus' Guardians were infected with during the Sky Ring Battle. It causes paralysis so severe, even standing will become difficult. Also, the burning pain will intensify over a 30-minute period until they die. It's so strong, it could incapacitate a wild elephant, but Hibari was able to overcome being restrained. The only way to remove the poison is to place the Vongola Ring in the hole that are in the wristbands that each guardian is wearing.