Gekido is a series of beat ’em up created by Naps Team, released on the Playstation and GameBoy Advance. A GameBoy Color version of Gekido was developed too, but the only proof of its existence is an old page on the official Naps team website and some lines in wikipedia. There are no cartdidges on Ebay, no ROM floating around the web, no review available, almost no screenshots… we can speculate that Gekido GBC was never published for some reasons.
Gekido for the PSP was also in development but never released.
Thanks to whitestrider for the contribution!