>>23578833
>Like, if there's the presence of mecha, why can't they build X or Y structure with it?
Simple solution: accept it and justify why they can build good castles everywhere
The difficulty is just to limit the number of mecha.
>If they know how to build this, why can't they build that? Who has the knowledge of these machines?
NOW that's the hardest part of any setting and what you should focus on.
There are many paths you can take, I'd only ward against the "Lost tech" option for a fantasy mecha, or any solution that do not allow factions to do their own maintenance.
My personal attempts (go ahead and steal)
Giant-animal = big power crystal = rare (human worship the animals and absolutely need them to breed)
Said crystal boost a single creature spell. Including a spell that is basically a telekinetic field letting caster carry or push against everything they want... now scaled up.
But! but! but!
That energy field is visible and hitting it with any slightly magical weapon provoke excruciating pain to the caster. Floating toward a castle will just have you faint of the hundred of arrows, or the few ballista bolts you'll take in the face.
...so in theory the best way to fight is to use that telekinetic field so the cast lift himself into an armor that roughly fit his humanoid magical shape.
...also removing the need for any mechanism more complex than hinge since they are basically big puppets.
Using that same basis, I also limit simultaneous spell to prevent mecha that both float and fight. Grounded!
>Secondly, you get pushed into learning a lot about the medieval world, titles, rights, differences between dukedoms, and fiefdoms etc
Indeed.
>I don't want to grift off /m/, but feel free to throw any suggestions for things you like to see, or would like to see in this sort of setting.
Don't ever feel bad about this.
All author "copy" what inspired them first in the first place.
GOOD author "search" better tropes that would serve their objective the best.