The retro Mega Man style was a very creative approach for this game, especially this type of game! The music and graphics are nice. I would be curious about some way to help Yuuka scale up faster with active play in the earlier game, although it's not vital for an idle-type game.
As for other ideas, there is definitely plenty of room in this formula! It's not a necessity by any means, but if the game was to be larger, the Mega Man formula led me to imagine that perhaps Yuuka could have different weapon types, or more idling defenders such as Wriggle. Conveyors to help the bees gather the inevitably overflowing bolts could improve collection.
Lastly, a way to save progress would likely be helpful. Idle games tend to be rather drawn out, so allowing players to return where they left off would let them use their time more efficiently.
Otherwise, as the others mentioned, it's a good take on "scale"!