The primary way Chen Fei currently increased his core soul energy was through daily cultivation, relying on the stimulation and nourishment provided by his techniques and elemental energy, allowing his core soul energy to naturally grow.
Because he had perfected three techniques, the efficiency of using elemental energy to nourish his core soul energy was much higher than that of an average cultivator in the intermediate stage of Aperture tempering realm. He was on par with those in the later stages of Aperture tempering realm.
As for the elixirs that could replenish his core soul energy, Chen Fei occasionally managed to buy them once or twice, but most of the time, they were out of stock. Over time, Chen Fei stopped putting too much effort into this area.
These two methods were the most common ways for most cultivators to increase their core soul energy. In simpler terms, it was a matter of accumulating core soul energy over time.