Bullet
What's like a bow, but even more simple? A bullet. With a bow, you have to load an arrow and pull back the string and aim, yuck. Bullets can be shot with just a simple squeeze of a trigger.
だん
ひ, はず, たま
None
If you want to shoot bullets, you need to do it at dawn (だん). Back in the old days, it wasn't bright enough to shoot arrows at dawn, but you can shoot bullets at dawn because they're simpler to use!