One must ask. How does someone with a extremely powerful ability, such as Sakuya lose to someone like Youmu for example. Youmu being a half ghost who wields two swords as Sakuya being able to stop time. So, pick one of the three.
A. Eirin’s shady drug.
B. Yukari’s fooling around again.
C. Everyone is drunk.
None actually, although there’s no real canon statements on who is more powerful then who, its usually a common conception that Fairies tend to be the weakest and humans usually can’t stand up to Youkai. But with everyone following the spell card rules, we don’t have insane fights that tend to resolve in the destruction of Gensokyo as a whole.
Everyone has to fight following Spell Card rules, therefore you hear all the famous names such as Icicle Fall or Fantasy Seal. Although there’s been a lot of fanon interpretation on how spell cards can be used. Or maybe that’s just to make things more interesting. But since I haven’t finished my homework yet, not going to go into too much detail.
If anyone is interesting, check out a fun new game called… Kamidori. If you were fond of Recettear but wanted more character development rather then shop keeping then you might like this better.