The Youjo Senki universe has at least 2 numeral systems, one “Roman” system where 10 is represented by “X” (though their “X” is different from the X in their alphabet) which is mainly used on clocks (and in the episode numbers) and an “Arabic” system that includes a 0 that is most obvious on some of the maps.
Interestingly, their “Roman” and “Arabic” numerals are identical aside from the 0 and 10. This doesn’t lead to confusion between, say, 2 and 11, because of the mandatory ligatures.
There are some instances of mixing both systems, such as “X000” – which supposedly means 10.000. This looks like a really bad idea, because by allowing a mix of both systems, XI could refer to both 11 and 101…
To add even more confusion, there is one clock with “main universe” Roman numerals: