Very nice game idea! Fits the theme and special object too!

You did great with the classic puzzle game mechanic introductions to make it understandable! 

Biggest problem I had was legibility, The text doesn't pop out enough. Level 3 was hard for me since I didn't understand/remember that the empty boxes can be filled. The background for them is the same as the normal background so I got confused. I think a different texture/colour for an empty box would make it easier.

In terms of game feel I wish it was easier/faster to fill a whole box, it's kind of a struggle right now and not enjoyable. Simplest fix would be a bigger brush size. But the best solution would be an automatic animation to fill it up (As in it doesn't matter where in the box you're drawing it's gonna fill it the same)  Also some sound would make filling the boxes feel more satisfying

The concept has a lot of potential, I'd gladly play more levels with the same idea!

Interesting puzzle game! Quite original Well done!

I think this idea has a potential, I liked the theme and special object implementation but the font and visuals are a bit hard to distinguish and understand.

Also I would be happy if you can play and give feedback to our game: GravLine