 If you liked
Ryuusei no Rockman
|
 ...then you might like
Accel World
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The concept of fighting in other worlds is similar, with just a small difference. Characters "Wave in" or "Burst Link" themselves to a world that mirrors the real world, while being something completely different that masks their identities while in the other world.
Not only is there a similar world concept, but fighting each other is present as well as gaining unique abilities from battling experience or even from each other.