The upgrade progress of the Cave had reached 46%, barely over halfway, but even this modest advance was achieved only after Dong Tianyu had fed it quite a few mystical items and resources containing Spiritual Ore Veins.
Since the level of the Cave mansion had stepped into the realm of Cave, it seemed to possess the ability to absorb the energy of the void and grow automatically. However, the energy converted by the Cave wasn't that plentiful, only enough to sustain the natural consumption of the creatures within.
It should be noted that, in addition to the purchased livestock, Walker Violet and Jasmine Anderson's Canaries also resided inside. Originally, if those Canaries didn't cultivate, then the upgrade progress of the Cave would have been a tiny bit faster.
But as they learned to cultivate, the energy converted daily was just enough for their practice and absorption, and to expect more Spirit Energy was hardly feasible.