In the world of A Record of a Mortal's Journey to Immortality, whether cultivators had to undergo a Thunder Tribulation when advancing depended closely on the spiritual energy density of their realm.
The Upper Realm was rich in spiritual energy. Human cultivators needed to undergo a Minor Heavenly Tribulation every three hundred years merely upon reaching the Nascent Soul Stage.
Meanwhile, the Lower Realm's spiritual energy was thin. Human cultivators did not even need to undergo any Thunder Tribulation to reach the Nascent Soul Stage, let alone Core Formation.
Although the thunderclouds above the nameless island appeared alarming, they were merely phenomena produced when a cultivator advanced to Core Formation. No true Heavenly Thunder would descend.
Of course, thunderclouds were only one of the phenomena produced by Core Formation.
After the dark clouds gathered, the spiritual energy within several dozen miles suddenly became turbulent.
Streams of spiritual energy surged together like flood dragons, converging madly from every direction.
In an instant, they tore open a massive spiritual energy vortex spanning several miles above the nameless island.
The violent spiritual energy continuously battered the surroundings, causing the flying boat beneath the three women's feet to lurch violently, nearly overturning.
The beautiful woman controlling the flying boat was greatly alarmed. She hurriedly formed a hand seal and barely managed to steady it.
The sudden jolting frightened the two girls aboard until their faces turned pale. They could not help embracing each other, their little faces bloodless and red lips trembling as they looked toward the beautiful woman ahead.
"Ma... Martial Aunt, what is happening?"
"Do not panic. It is merely a spiritual energy current."
While stabilizing the flying boat, the beautiful woman explained with feigned ease, "The spiritual energy on this island is too scarce to provide sufficient energy for Core Formation,