Syvalion is a shooter that was released in Japan, and in Pal regions. It is currently unknown why it was unreleased in North America, as it was translated to English for the Pal regions. Perhaps the game was too mediocre and short to warrent releasing it. According to the half.com page, it was supposed to be released in February 1992. The game was previewed by Nintendo Power in their April 1993 issue, so the previous date is likely in error. The publisher was to be JVC.

Screenshots from Nintendo Power, issue 47 (scanned by Retromags)

Box from half.com