This achievement requires you to play on every stage available (including the unlockable Slash and Reload ones) in the game at least once. Apparently this achievement only applies to VS CPU mode.
Playing matches in any other Mode in the game, will NOT count towards this achievement. All stages must be played in VS CPU mode only.
It has been confirmed that you don't actually have to finish a match on every stage. It still counts if you just start a match, hit start, then go back to Character Select immediately to play the next stage. For those who want to play on the safe side, you can select Ky Kiske and perform his Instant Kill just to make sure they count. Credit goes to DarkSephiroth for the quit to character select confirmation.Unlocking Stages
To unlock all Slash and Reload versions of the stages you must complete all Story Mode paths for the majority of the roster in the game. To be safe, just attempt this achievement after you unlock "And to the introduction".
By then, you should have all stages unlocked. To unlock the "Unknown" stage,
be sure to complete Arcade mode at least once with any character such as I-No for instance.
When scrolling through the list of levels, you may see some duplicate stage names. This is because there's basically 2 consecutive lists of stages in a row, the only difference being the picture representing them. Below is a full list of stages, starting with the London stage that shows a picture of a bridge. The first list has stages with red names. The second list has stages that also have red names but if you hold Respect [R-trigger], the stage name turns yellow. The Slash version of the stage is the stage you get when selecting the stage normally with any button, in other words, the normal version of that stage. The Reload stage is the stage you get when you hold down RT and select the stage with any button. You need to start a match on all of these stages, and there are 47 in all. Make sure you keep a checklist of these and check them off as you go
The stages are Red and turn Yellow by holding RT. You must play both the Slash and Reload version of each one.
(This list starts with snowy London scrolling to the right)
Frasco (Red only)
A.D. 2172 (Red only)
Grave (Red only)
Heaven (Red only)
The achievement will automatically unlock once you start a match on the final stage needed.