I think I already know most of them, but here goes:
I'm not certain, but I think his hero stance is mostly Kazuya Mishima. I know the hero stance is based around Tekken but I'm not sure if it's more than one character or not.
His ninja stance is an amalgamation of characters from Mortal Kombat. The down triangle is based on Smoke, the forward triangle is based on Sub-Zero and the neutral triangle is based on Scorpion. His bicycle kick is based on the same move Liu Kang uses.
His oni stance is pretty much Akuma. I thought it was Ryu at first, but the aerial mochi attack is the same thing as Akuma's aerial hadoken. This is further evidenced by his level 3 mimicking Akuma's raging demon and the fact that oni means demon in Japanese.
Any errors or omissions? Discuss.
His Oni stance is very close to Akuma. He even has the dive kick.
Justice stance reminds me a little of Akira from Virtua Fighter. He does have Ryu's donkey kick though..
Ninja stance is obviously Mortal Kombat inspired.