@Acolytus
I think it is a wall of language that the author already know. Each language doesn't have an equal spelling.
For example, I'm Thai and can't spell TH sound correctly unlike western. In the same way, Japanese can't spell Romeo correctly cuz they don't have a "long" sound. Most of words in Japanese ends in short, so it isn't weird to see Romio instead of Romeo.
I think his mom wants to give him western name like Romeo, but due to the language limit, you can't spell Romeo without shortend it to Romio.
That is how it works in general.