Mario = Reimu, Peach = Kaguya, Bowser = Suika, Luigi = Sanae
Yoshi = Kogasa, Wario = Rin, Donkey Kong = Yuugi, Diddy Kong = Tewi
Link = Momiji, Zelda = Patchouli, Sheik = Sakuya, Ganondorf = Nue, Toon Link = Lunasa
Pikachu = Iku, Pokemon Trainer = Rinnosuke, Squirtle = Suwako, Ivysaur = Marisa, Charizard = Hatate, Lucario = Meiling, Jigglypuff = Kyouko
Kirby = Yuyuko, Meta Knight = Remilia, King Dedede = Miko
Fox = Ran, Falco = Mystia, Wolf = Ex Keine
Captain Falcon = Mokou, Samus = Utsuho, Zero Suit Samus = Nitori, Captain Olimar = Alice
Ike = Tenshi, Marth = Youmu, Lucas = Yuuka, Ness = Satori
Popo & Nana = Letty & Cirno, Mr. Game & Watch = Eiki, Pit = Byakuren, R.O.B. = Reisen
Snake = Kanako, Sonic = Aya
I came up with this when I was bored a while back, replacing each SSBB character with a Touhou character who I think can be related to them. Some like Reimu, Sanae, and Momiji should be obvious, but some... Below are some that I think most people won't get why:
Yoshi/Kogasa: Tongues.
Wario/Rin: Ram your enemies with your wheelbarrow/motorcycle!
Diddy/Tewi: The former throwing banana peels makes him look like a something a prankster like Tewi would do.
Ganondorf/Nue: Nue having a trident makes me think of Ganon and his trident.
Toon Link/Lunasa: The former's Wind Waker makes him look like a musician, and Lunasa is one.
PT/Rinnosuke: They don't fight by themselves. The latter never even got into a fight of any kind, I think...
Ivysaur/Marisa: Simply because Solar Beam and Master Spark (as seen in the former's FS) look a lot like each other.
Charizard/Hatate: Ran out of other winged characters, and I want to use only Windows ones...
Jigglypuff/Kyouko: Sound-based powers.
Meta Knight/Remilia: Bat-like wings.
Dedede/Miko: Royalties, even if the former is self-proclaimed.
ZSS/Nitori: I'd imagine the latter's mechanical arms to act like the former's plasma whip.
Ike/Tenshi: The latter has a move where she stabs the ground, just like Ike, right?
Lucas/Yuuka: Both are associated with sunflowers (the former through his mother).
Ness/Satori: Mind readers and can talk to/communicate with animals.
Mr. G&W/Eiki: Black and white
Pit/Byakuren: Both are "holy".
R.O.B./Reisen: Eye beams!
Snake/Kanako: Snakes, snakes!!!! SNAAAAAAAAAAAAKES!!!!!!!!!
Also, when I think about it, Byakuren's play style would be more similar to Ganondorf's, while Nue's more like Pit's. Think about it...
And while we're at it...
Dr. Mario = Eirin
Young Link = Daiyousei ("fairy boy" and fairy)
Pichu = Nazrin (rodents)
Mewtwo = Yukari (one of the most powerful characters from their own series)
Roy = Flandre (fiery weapons)
The Light Arrow though does not match
Throws a knife that zips across the screen very fast?