This is such a cool game!
The main mechanic is highly polished across all aspects: game feel, art, audio, feedback, everything. That makes it so satisfying to complete a loop and it adds to that "I want more" feeling. Really well executed!
The synthwave aesthetic I think is an accurate decision for a game about drawing lines. It makes for great synergy.
It's a no-brainer for why this idea fits into the theme. Yet, despite being simple, it's so well executed that instead of lessening the experience, it actually adds to it. That's a cool lesson to learn as a jammer.
I only found one balance issue which was that bosses were pretty easy to beat if I drew giant rectangles that fit the entire screen. The only boss that gave me trouble with that was the last one because it spawned little corruption circles. Maybe a similar strategy in a lessened version can be applied to the earlier bosses? Or maybe it can be fixed rule-wise (you can't make loops that are too big).
Other than that, very solid entry for the jam. This is a great game.
Congratulations!