The Autumn Valley.
Upon returning to the Autumn Valley with He Mengxi, He Jin personally went to the strongest mid Dharma adepts in the Autumn Valley, while he asked He Mengxi to look for Zhou Donghuang.
Although Zhou Donghuang had not displayed his power since attaining the mid Dharma stage. He Jin was sure that Zhou Donghuang was definitely training in a supreme technique that had allowed him to be as powerful as a mid Dharma adept even when he was just in the early Dharma stage.
Now that he had attained the mid Dharma stage, he was definitely stronger than ever.
At the very least, in the Autumn Valley, or even in the Lightning Sword Sect, it would be difficult to find a mid Dharma adept that was his match.
He Jin did not know that Zhou Donghuang was currently training using the "Way of the Four Supremes," which could only be considered a Primordial Soul technique that only allowed him to train up till the Primordial Soul stage.
