Just putting it out there, eventually everyone will reach a wall, and everyone will be able to get the fremium characters. This is far from Pay to Win, and more of a Pay to Advance. Sure, you make a gap quickly and efficiently in the beginning, but those few players who actually play the game will not be let down. I hadn't spent more than $50 on the game (Jounin Medal), and I've been consistently in the top with players who spend FAR more money than i do. I'm also close to getting Sakura, and should be able to get her finished with the next time her event runs around. Playboy should be done soon. A lot of the non fremium rare characters I've gotten from playing trials.
TL : DR - I've only payed for Jounin Medal, and I'm keeping up with players who have went hams to the wall and bought everything that came out so far, only lossing to the "Immortal" Water/Sakura team combo.