Will add that I consider Raiko the most fun extra boss fight.
For the rest… that’s hard to say, too many options…
Clownpiece is definitively the most memorable stage 5 boss tho, or perhaps boss altogether. That will most likely not go away.
Oh and for playable characters I’m an unconditional fan of Marisa, but they’re all pretty fun in their own ways.
Edit: Here is my explanation of the touhou plotlines :
TOUHOU PLOTS
EoSD : A maid wants to take her master out for a walk.
PCB : A ghost wants to know who’s buried in her backyard.
IN : A sadistic doctor is hiding a NEET. And the moon.
MoF : A snake wants fantasy creatures to believe in gods.
SA : A nuclear chicken build an exhaust pipe.
UFO : An UFO revived Jesus who got shipwrecked in a landlocked land.
TD : ??? (didn’t play it)
DDC : A midget leads a rebellion of sentient objects.
LoLK : An american flag scared bunnies.