The 33 Heavens are the 33 remaining traitors left from the 3000 Lower Realms that the Paragon Immortal Realm ruled over. They stay outside of the Mountain and Sea Realm to act as 33 Seals that seal the Mountain and Sea Realm. The 33 Heavens are inhabited by beings known as "Outsiders".
Book 8 Edit
After the war with the 33 Heavens began, Meng Hao destroyed the 1st Heaven, which unlocked the will of the Mountain and Sea Realm and allowed all of the cultivators of the Mountain and Sea Realm to experience cultivation breakthroughs. Thus, it can be inferred that the destruction of the rest of the 32 Heavens will have similar effects.
When the war was brought to a close, they again created a new 33 Heavens that once again locked down the Mountain and Sea that was brought to the Green Coffin Vortex.
Book 9 Edit
After 2000 years since the settlement of the Mountain and Sea Butterfly in the Green Coffin Vortex, the 33 Heavens gained four 9-Essences Paragons. These include Dao Fang, the middle-aged man that was an 8-Essences Paragon and fought Meng Hao, and two new 9-Essences Paragons groomed by the Immortal God Continent and the Devil Realm Continent. However, none of these four was a true 9-Essences Paragon as the dao of their ninth essence was forced upon them and was not their own dao. This made their battle prowess plummet and it would require all four of them to battle a true 9-Essences Paragon.
Destruction of the 33 Heavens Edit
After the return of Meng Hao, along with the entirety of the Vast Expanse School, Patriarch Godlizard, the Holy Termite, and the Primordial Patriarch, the 33 Heavens learnt of the deep resentment and hatred that Meng Hao had for them. Meng Hao decreed that all of the cultivators of the 33 Heavens be slowly and excruciatingly killed in body only and their souls be captured. He told his subordinated to take their time and spend a day on slaughtering the denizens of each of the 33 Heavens. During this time, Meng Hao tortured Dao Fang before pulling out his blood and soul to kill his bloodline, successors, masters, friends, and anyone who had Karma with him (basically anyone he knew) before finally throwing his soul in a burning hell to be eternally tortured. After reaching the 15th Heaven, Meng Hao told his subordinates to stop and threw all the souls collected thus far into the same burning hell. Then, Meng Hao brought out the other three 9-Essences Paragon who were attempting to flee. The two new 9-Essences Paragons were flayed alive and then left to burn, while the middle-aged man was taken by Meng Hao and his head smashed on the landmass of the 15th Heaven, repeatedly.
The 13th Heaven, especially, enraged Meng Hao as this Heaven could be said to have been the hub of the trafficking market of the 33 Heavens. During the fall of the Mountain and Sea Realm, many cultivators and mortals were unable to make it on to the Mountain and Sea Butterfly and were enslaved by the Outsiders. These unfortunate beings lived a life far, far worse than death. Women were sexually used, broken, and discarded. Men were made to live the lives of dogs. And children... were eaten like a gourmet meal. Meng Hao uncovered a huge pit on the 13th Heaven which was littered with bodies of the denizens of the Mountain and Sea Realm. These bodies all, without a shred of doubt, had bite marks indicating a cruel death. Here, Meng Hao used the daoist magic that Allheaven had used on him outside the Vast Expanse and had the Outsiders killed by the Mountain and Sea Realm people they, themselves, killed.
Meng Hao stopped once he reached the 10th Heaven, and told all the cultivators of the Mountain and Sea Butterfly to come and take their own revenge. This was to allow everyone to let loose their pent-up hatred. He also suppressed the Outsiders which made them unable to fight back, resulting in zero casualties to the Mountain and Sea Butterfly cultivators. Afterwards, the 8th Heaven was revealed to be the traitorous Ninth Sea. One can only imagine the fate that waits the traitor who caused an anomaly to occur in Shui Dongliu's plans which resulted in his, and thousands of others', death.