This is from Yuki-onna:
Mosaku no kao ni iki wo fu-tsu to fukikaketa.
The "fuutsu/fu-tsu" is written in katakana and is most likely an onomatopoeic word, related to breathing. It's not essential to the translation, but it's really bugging me.
This is either a typo or a "reado".
Trying to reconstruct the original sentence from your rōmaji version, I'm guessing it is
フーッと is listed in some dictionaries (e.g. WWWJDIC)
with a whiff; with a puff
The ッ is small (compare ッ and ツ) and is geminating the following "t" sound. You're correct in assuming it's an onomatopoeia and it's usually used for the sound produced when breathing out (either forcefully, or with a sound).
The romanization would be fūtto (and not
There are other onomatopoeic words that follow this pattern. Either they are written in all hiragana, or in katakana with only the と in hiragana:
or more generally also