The environment constructed by this domain resembles the inside of an active volcano. It is a sealed-off stone chamber with large fissures across the walls and the ground that spout large portions of magma. This produces an ambient heat so great that the average jujutsu sorcerer would combust upon entering the domain.
Coffin of the Iron Mountain is a lethal domain that includes a guaranteed hit. The user can command molten rock that extends from the environment to hit their opponent with a can't-miss attack.
Jogo first displayed his Domain Expansion when he was desperate to kill Satoru Gojo in their fight. In order to bypass Satoru's Infinity, Jogo needed to employ his can't-miss attacks. While a normal sorcerer would burn up inside Coffin of the Iron Mountain, Satoru was unharmed and was able to protect his student, Yuji Itadori from the heat as well. Satoru countered Jogo's first attack by blasting the guaranteed hit with his own jujutsu.
Determined to leave Satoru burned beyond a pile of ash, Jogo attempted to ramp up the cursed techniques. However, Satoru expanded his Unlimited Void, which proved to be the more polished of the two domains, and quickly suppressed Coffin of the Iron Mountain. Due to this defeat, Jogo didn't even attempt to use his Coffin of the Iron Mountain in his battle with Sukuna, afraid that his opponent's domain would overtake his own.
- Gaikan (蓋棺?) refers to the lid/lidding of a casket.
- Tecchisen (鉄囲山?) comes from the legend of "nine mountains and eight seas" of ancient Indian cosmology, which exists in Hinduism and Buddhism. The legend speaks of the mountains and seas that constitute the world—the nine mountains are Mount Sumeru at the world's center and eight concentric mountain ranges surrounding it, with those nine being in turn separated by eight seas. The outermost mountain range, forming the world's circular periphery, is called Chakravāda-parvata (Japanese: 鉄囲山 tecchisen/tetsuisen?) due to being made out of iron, unlike the other mountain ranges that are made of gold.