This is such a ridiculous plot element. If the spiritual qi is essential to life, then a healthy living organism should simply regenerate it. I mean, where the heck did it come from originally? I'm pretty sure for a new human (or other creature worth noting) to be born in that universe as well, all you need is a sperm cell and an egg cell. No ultra rare fruit or fungus is needed as the third component when a husband and a wife are planning a family increase. Otherwise there would be no people in the first place. Sure, I could accept it would take time and be troublesome, like lying on a mountain naked for a year, but that's it. As it is, this is too artificial.
I bet the Soul Clan can fix an issue like this in a jiffy just by transferring spiritual qi from some hapless victim to the one they are trying to cure.