Long ago, the Grongi Tribe terrorized the Linto (リント Rinto) until a warrior named Kuuga appeared and defeated the Grongi, sealing their leader within a cave. In the present day, a multi-talented boy named Flash Sentry finds himself linked to the mysterious stoned belt that was found within the excavated cave as the Gurongi are resurrected and resume their murderous game on the descendants of the Linto, humanity itself.

It is up to Flash, along with the assembled Science Police, to use the various powers of Kuuga to stop and defeat the Grongi Tribesmen from their continuous killing and ensure the happiness of others. However, as the endgame draws near, Flash learns that there is a horrible revelation behind Kuuga and the Grongis' leader.