Anvelope
Inala doesn't have a tertiary nature. That's a good thing. Now if he dwells into the data of cultivation system of body and soul. He can create a powerful tertiary nature for himself.
I think the one who will discover other aspect of the human cultivation system is either boul or virala/ruvva. boul i think he will find out clues about it when researching the brimgan empire accumulation to perfect their new mystic cultivation technique. virala/ruvva when they are researching a cultivation technique that suited mystic human or when they're perfecting mystic Sumatra virala got years ago. Inala is also a candidate but for now idk what he will be doing to come across it