Congrats on finishing your game for the jam! Well done
The use of theme here boils down to randomized rewards after each wave. That's a fun take on the theme, but I could see it getting a little impractical for tower defense games as these games are really make or break on the balance. I think I needed a little more information up front about each tower's range - maybe show the range when you're hovering a tower before you buy it?
I lost pretty quickly, but I still had fun building up those towers. The catapult seems too slow to ever be useful though, especially when it's the most expensive. It just didn't feel good to buy.
Games like this thrive off giving the player as much information as possible - damage numbers, range indicators, wave counts, etc. Tower defense is a favorite genre, but it presents a lot of challenges for a game jam, especially in just 48 hours. Great job overall.
Keep making games!