That quality is shikigami-like itself - it supposedly didn't used to be this way, but a shikigami is created by infusing something else with magic or... something like that. I don't know how that works. At any rate, for magical servants some of them can be quite independent.

[Touhou shikigami are not... exactly like classical ones.]

Although I'd guess you're still weak against water, though. It would explain why we hadn't seen you on the beach, and that's another thing the two have in common.