I have just finished the game. :)

Some on-the-fly remarks:

1. The two little squares are cute. :) The ‘evil moustache’ has a funny classic older cartoon vibe. ^^
2. Controls are QWERTY-only instead of layout-independent, while the arrow keys are not enabled. So, a bit complicated with my AZERTY, especially as here, some select movements are critical! It is possible to program keyboard keys in a position-based manner.
3. Nice and clear presentation of the tutorial.
4. Although you can restart a level by running into a red crossed tile, I think a key for restarting would have been useful.
5. The core idea is clever. In particular, there is a clear use of relative shift using blocking blocks (! Is that a pleonasm?). (I cannot help thinking of my own game which I was not allowed to resubmit here, sorry. XD But amongst the things/mechanisms you have to think about to solve the puzzles is precisely this concept of getting to shift your ‘dual’.)
6. I have just finished the six levels! :) It is enough to see the concept at work, considering there was no further mechanic to see.

The concept stands out. I think the game in its present state serves as a prototype that demonstrates how the main mechanic works against the ‘shift-by-blocking’ tool the player has. It is possible to design more complex levels, but I think yours already force to think ahead and even sometimes count how many tiles ‘away’ the two playable squares are.

Suggestion: it would probably be very interesting to extend the game through other compatible mechanics; example suggestions: teleporters; switches that open/close doors. (… or activate/deactivate lasers, if I refer again to my game. X) You may want to check if you could not be inspired by how its mechanics work!)

(And as a last coincidence, I also chose blue and red as the main dual colours! XD I realized I often do, eerily enough. This may be related to some primal perception of these two colours.)

If I wanted to nitpick, I would say that the squares are rather friends than enemies, because they are together in this! ;) But it’s true that any one square can make the other go into trouble, so in fact, I think the game is well related to the constraint.

Sweet idea and nice implementation. :)

I really enjoyed the gameplay more than I though, and it's harder than I though too.

The puzzle is well done and the gameplay loop is also well craft.

The sound is nice and simple. Art still has some room to improve. Lighting and effects might take a lot of time, I guess.