They're of varying types. One of them is here with us in Luceti, a shrine maiden by the name of Reimu Hakurei. She isn't much for training, though - most of her power is hereditary.

In fact, many of the strongest people there, be they human or youkai, are somewhat lazy. The only two I know of that are exceptions to that are a vampire and a human magician by the name of Marisa Kirisame... the former I am not particularly fond of speaking of, but the latter is arguably the strongest human in Gensokyo, next to Reimu.