I'm talking more about C (or any low level stuff) than Unicode now. The world I'm using as a reference has only byte arrays, smokes and mirrors.

I'm constantly pointing you _to the awk codebase_. It's a relevant context, the title of the post and it matters. Can you please stop ignoring this? There's no Unicode library there, it's an implementation from scratch.

If you are doing it from scratch, there's a part of the code that will deal with raw bytes, way before they are recognized as Unicode things (whatever they might be).

Ever since this entire post was created, the main context was always this: an implementation from scratch, in an environment that does not have unicode primitives as a first-class citizens. Your string functions don't have \u escapes, YOU are doing the string functions that support \u.