"Hyuui" may look strange, but this is just the way they write "Huey", which is not unfamiliar to English speakers.
And don't underestimate a reader's ability to understand or get used to words they are not initially familiar with.
As I had said before, kids (at least in Mexico and Latin America) did not have problems using Japanese names in Mazinger Z.
Although (if memory allowed), I would have loved the UI of the PS games to show a description of what the spells do. Remembering (or discovering) that may even be more problematic than using the spell names.