Welcome and hello 13org! Kingdom Hearts reference by chance?

That's a good question. Alright so tech-wise I haven't done a deep dive into what was available around when cannons were invented but we can start with cannons as our basis for technology (The Metal Fireworks weapon mentioned towards the end of the prologue are meant to be a description of a cannon). 

Anyway, my brief google search tells me cannons were invented early 13th century, so early 13th century we can uses as our starting point. Gunpowder has recently been Invented by the Nation of Hearing so there aren't a lot of weapons that use it yet and we are some ways away from having guns. The tech level does not have to correspond exactly with Earth's tech level was during the early 13th century. Spectacles were created in the late 13th century which is within range. The one invention that I mentioned which is not in range however are spyglasses (17th century I think). I obviously didn't do my proper research there, oops. I figured if they have spectacles, then why not spyglasses? Oh well. Anyway that just means better quality glass-work can be a thing. If you are unsure about certain technology, just run it by me. 

Let me know if that helps.