A lone H in Japanese words is a holdover from phonetic mistranslations that were common in the 1980s and 90s.
What it means is that the written Japanese for Goku translates (in Hepburn) to “Go Ku U.”
The last U means the speaker holds the end of Ku a little longer. This is different from a full-width dash ー meant to extend any sound that came before it, it’s an actual separate character that can be written as う in Hiragana (phonetic Japanese characters) but won’t always be seen when reading Kanji.
In the past, the presence of the U sound after another sound was often miswritten in Roman letters as H because that’s what it sounds like to a lot of people.
Example: Touzai used to be written Tohzai because to the western world, the latter is what it sounds like.
But these “extensions” of a sound can also be written with an accent dash over the previous vowel when written in Roman characters to make the word more readable.
Tokyo is actually suppose to be written Toukyou (To U Kyo U), if you look at the Hiragana spelling of the Kanji. So as a compromise, you can write Tōkyō to properly represent all the sounds presented in the original Japanese word.
(I am far from a Japanese teacher, but this is what I’ve learned over the years.)
