Reimu is nice when she's taking it easy and doing what she wants to do. She gets all bitchy when some big-shot youkai starts shit and she has to stop taking it easy and go solve things.
shinmasaki said: Either I've been wrong about Reimu all this time, or this is an imposter. I really hope I've been wrong about Reimu all this time.
It's hard to tell, mostly because ZUN himself is so damn inconsistent with her:
Its outright stated that her shrine gets little visitors (beyond youkai) because she's ostracized by many humans (though not all or even the majority of them) simply because she treats humans and youkai equally (if you cause trouble you get your ass kicked, if not she leaves you in peace)!! I can see where that would lead to bitterness.
But there are plenty of in-game examples (and even at least one manga example I can think of) of her acting almost racist against youkai (assuming they are causing trouble just because they are youkai)!
Yet this also contradicts the canon fact that many of her previous foes hang out at the shrine and she even put up with Suika the moocher, all with little complaint on her part!
If anything, her worst antagonists have always been those who are supposedly aligned with heaven or of divine status! The Moriya Shrine crew specifically wanted to put her out of business (and later indirectly caused the events of Subterranean Animism and Undefined Fantastic Object, and Kanako is canonically stated to be planning to make Gensokyo as much like the outside world as possible) and Tenshi destroyed the Hakurei Shrine and is one of the few to canonically defeat Reimu! She gets more trouble from gods and celestials than she does from youkai!
actually most of extremism associated with the Moriya shrine is mainly Sanae's doing as in MoF's endings, Kanako reveals she merely wanted to talk (and Sanae decided to help out an ailing shrine)
Though some games have cases where the Reimu and other Heroines act particularly jerkass before a fight (but end up making nice afterwards); mainly UFO and IN, where Kaguya in one scenario, comes off as more heroic than the player characters.
But Reimu does have nice moments, such as in the three fairies manga where she warns a fairy (that looks alot like Daiyousei) to go home before the upcoming storm blows her away.
And the shrine problem is also caused by the route to it becoming ill maintained and dangerous.
various canon side materials and endings do paint an interesting picture of Reimu.
One thing is that a lot of what's said before the spell card duels is posturing and bluster. It's part of the whole system of them being a replacement for actual fights, so you get deadly serious banter before the dual starts to get things in the right mood.