Things might go this way:
Main games: playable characters are more or less human (the youkai only assist them)
Decimal shmup games: playable characters are NOT human
Decimal fighting games: playable characters are whoever ZUN wants to put in, the criteria followed by those who get in story mode vary
I think the PC 98 criteria for playable Touhou characters should be ignored as it is more or less irrelevant by now.
No idea how things goes for phantasmagoria games, though
All right, while this seems to be true there are many things we gotta take into consideration, first of all there are multiple ways to categorize an incident and it's related to the plot/type of game.
First there are the main incidents, which most of the time happen and can spell trouble if left unatended, these incidents tend to be solved by the main characters which are mostly human, like stated before there is a symbolism regarding that, humans solve incidents (most of the time) and youkai cause them.
Next come the incidents that although, do not pose a threat to Gensokyo affect many of it's residents
incluiding youkai, for example SWR in which Tenshi placed a seal on most of the people from the cast or PoFV, where during the flower viewing many things happened which led to even youkai trying to figure out what is happening (although, in the end remember that no one solved this incident, not even Reimu)
PoFV was a special case because if you read the characters profiles not everyone wanted to solve the incident, for example Reisen was trying to find Tewi. This actually applies to many playble youkai in multiplayer games, for example in HM Koishi just wanted to be noticed. Rarely youkai want to solve incidents but they certainily do when they feel like it, that's the whole plot of SA
youkai tried to solve an incident but they could not go underground on their own.
However I think it's mostly because ZUN wants to keep that previously stated "barrier" that youkai cause incidents and humans solve them, meaning that even if a youkai needs to solve an incident one way or another humans will be forced to solve it
The fighting games certainly were. PoFV was an incident, too. For the photog games, it's debatable - Aya asking random youkai and humans to do their best could be an incident, in a sense, not to mention the arrival of Hatate and her whole rivalry thing in DS. I'd say ISC was probably breaking the Spell Card Rules in the service of a major incident to be resolved, but it sure opened the door for humans and youkai alike to be able to break that rule (if it indeed did - if it didn't, well, add that to the list of youkai-as-PC games where the rules still applied).
Again, I think we might be squinting really hard at the games trying to find a Human v. Youkai as playable character pattern where there isn't one.
It was not an incident because 1-It did not threatern Gensokyo safety 2-No one got affected by it. But Aya was a nuisance, right? Yeah, she was but that was part of Gensokyo daily life, incidents are out of the ordinary, even for Gensokyo. The rivalry between the tengus was not normal too, but it didn't affected anyone, just like Th12.8 was a conflict between the fairies it did not cause a real incident.
I would say that decimal games (that are not spin offs) are there to show us another side of Touhou, where an incident is not necessary to know that Danmaku is present in daily life.
Yeah, pretty much Youmu being half-ghost (I think including Sanae is a stretch; though a "living god" she is after all human). And I also think the solo peeps in IN being unlockable as opposed to there by default is iffy - plenty of youkai were unlockable in PoFV, too, and the individual non-humans in IN had their own personal stories in the game.
But, as I said, seems we only differ over a matter of degrees, so I won't be losing sleep over this. And though I don't have $100 to be throwing around over a wager, I'd be happy to make a friendly bet of some other form. Maybe a fanfic of reasonable, short length with the plot of the winner's choosing?
Yeah, Youmu is half human, I see what's Clarste point that in the end humans are the ones that solve incidents. But well, for the sake of the series ZUN does what is the best for the plot, I mean, he did a game based on the manga (FW) and with characters that we would never expect to be in a game.
What if for the next game youkai are now in danger or something and we get to use everyone but Reimu and Marisa? Anything could happen when it comes to ZUN, even if there is a formula, I actually don't think our predictions for ULiL can even be accurate.
