American people and their fetish of putting h for no reason Noa -> Noah Nou -> Noh Touma -> Tohma lol wtf
For Tohma, at least, the Japanese Foreign Ministry authorizes it to be used on passports. It's also sometimes used in lieu of other forms. And, in American English, the "h" isn't pronounced, but it affects pronunciation of the rest of the word. Without the H, those words would very likely be butchered. Especially the "Nou" one. There's a reason "2hu" is a term of derision.
Source: I speak this damned language, and I have been for my entire life.