Over at the Lost Levels forums, user Johnny Undaunted has uncovered information regarding Tokeijikake no Aquario ("A Clockwork Aquario"), an unreleased arcade game created by Wonder Boy and Monster World series developer Westone.

A translated account of the game's location tests reveals that Aquario was a side-scrolling platformer with a mechanic allowing players to trigger temporary invincibility to plow through tough enemies. The invincibility mechanic was dropped in subsequent versions in favor of easier, simplified gameplay, and development was scrapped after multiple poor showings.

Aquario would've been Westone's final arcade release, following up on a series of lesser-known greats like Aurail and Wonder Boy III. The company shifted its efforts to console development afterward, producing the wonderful Monster World IV before succumbing to years of Japan-only dating sims.

Remarkably, Aquario's soundtrack was preserved thanks to composer Shin-ichi Sakamoto having a premonition of its negative reception, after which he recorded the game's music directly from the prototype arcade board. While the game itself may be lost forever, the soundtrack saw an official album release in 2006.