It's about these kids who go in a simulation and have to fight monsters and stuff. One of them is a samurai and another is a cat dude and the last is a guy who is not in the sim and is helping them. If you know what I am talking about, please help me.
I would put my money on Code Lyoko. Four children discover a supercomputer that they have to enter to fight against the evil AI known as X.A.N.A. When in Lyoko, Odd has a cat-like outfit, while Ulrich's costume resembles a samurai (or probably more a ninja). Yumi, the female member of the group, dresses as a geisha, and finally Jeremie never enters Lyoko proper but instead co-ordinates the group from a computer terminal.