The Fire Release: Heavenly Prison is an imprisonment technique (禁錮術, kinkojutsu) used by Mui's clan.
The ones who are subjected to this technique have a formula applied to them, which will prevent them from moulding chakra and from using techniques. It will also drain them of their chakra at a slow but steady rate. Mui uses this technique on the prisoners of the Hōzuki Castle. If the ones who have the seal on them leaves a certain radius from the applier, then it would cause the victims to burst into flames from the inside, burning them to ashes. The user can also ignite the seal at their own free will.
However, for people with high amounts of chakra, such as Naruto, they can still mould chakra and use techniques to a certain extent. The techniques used, however, will be severely hampered, and the seal will cause the user in question intense pain, as though their bodies were on fire; if too much chakra is forced out, the formula will set the victim ablaze.
Being a fire technique, it cannot work in water, and the victims simply has to submerge themselves in a body of water to use chakra with ease; anyone set aflame by this technique can be saved if water is poured over them. Also, this technique only suppresses normal chakra from within one's body; when enhanced with natural energy gathered externally, one is still able to use chakra. If anyone with the seal applied were able to create a shadow clone, the clone will not bear the seal. The seal will disappear if the user dies.
- Despite being seemingly bound by the Heavenly Prison, Maroi was able to use Lightning Release: Lightning Signal Fire and Water Release: Archerfish without adverse effects. This may due to Maroi gaining favour of Mui, thus negating the sealing.
- A caster of this technique can place a false seal on the victim, creating only the markings without the effects, as Mujō did on Boruto Uzumaki and Mitsuki, to allow them to enter the prison undercover. This may be what Mui did on Maroi.
- Despite Naruto being branded with this technique, when he transformed into Sage Mode, he was able to leave a great distance from Mui when Gamabunta escaped the castle to rethink their strategy without Naruto bursting into flames.
- The Ice Release: Earthen Consecutive Chains of Ice has been considered to be on par with the Heavenly Prison in terms of restraining prisoners, hence the reason its user was named Mui's successor as Hōzuki Castle's master.