You know, the "Wizard" setting, inspired by, I think, probably, Warlock of the Magus World, seems to still be around, every so often, like a fantasy version of xianxia, because the high end is exaggerated to a degree that makes you question if the writer understands scale just like xianxia, but unlike xianxia, I've never seen it combined with "Many Children Many Blessings" cheat yet
Essence (jing) is from the genitals or thereabouts, you get a chunk of it from your mother (specifically yin jing), and its refined into Qi within the Lower Dantian.
Qi is Qi. Its refined into Shen within the Middle Dantian and I have no idea what its about, though Shen has divine connotations and also means spirit and so on.