This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 釚 is uncertain. It visually combines 金 (metal) and 九, but the original semantic or phonetic role of these components is unclear.
Since the meaning is unclear, focus on the shape: metal 金 beside the number nine 九. Imagine a mysterious metal object marked with the number nine.
For ヒュウ, use the invented sound 'hyu' like a quick, sharp hiss of steam from a metal object marked with nine: hyu -> ヒュウ.