Mana
Mana was similar to Qi, but their nature and characteristics were different.
In the era of the mages, instead of Qi, there was mana, a crucial element that defined the mages.
Without mana, mages couldn't have interacted with nature and bent it to their will, producing heaven-defying effects that could render even a first-stage martial artist insignificant.
Mana was essential for forming a mana heart, the source of a mage's strength, yet also their greatest weakness.
Similar to a martial artist without a Qi, mage was nothing without mana. In fact, they were even more miserable than martial artists, as martial artists have stronger bodies strengthened by Qi, but mana didn't strengthen one's body.
However, with the fall of the mage era, humanity had to adapt, and mana underwent a strange mutation.
Its properties changed significantly, making it unsuitable for giving birth to mages and instead paving the way for martial artists to rise.