stands in for Hu sounds in words like Hoop and Hood. But that's not all Fu has to do, no. Like Vu does for V-sounds, Fu is compounded with other characters to make the other F-sounds used in loanwords.
Final Fantasy would be the obvious choice... but they've used Romanized titles on their logos since almost the beginning. So instead have a look at the Fire Emblem logo:
In the distant past we covered how sometimes an elongated A sound is used for "er" sounds in English, and that's why the kana for "A" repeats in the word Fire. It's the same thing with the other vowel sounds, with a small E for Fe, a small I for Fi, etc... and of course a small O for Kamen Rider Fourze.