This was to be a massive RPG which would encompass an impressive, Riven-esque five disks for the Famicom Disk System (a floppy drive add-on for the Japanese NES). By that point, though, the FDS was waning in popularity and Square lacked the resources to develop such an ambitious epic for a fading peripheral. The game was reportedly killed before it even got underway, and Square apologetically informed consumers that perhaps they should spend their money on the upcoming Final Fantasy instead. The company then slapped the Seiken Densetsu name on an upcoming GameBoy adventure — to save the expenses of registering a new trademark and hiring someone to do up a new logo, perhaps?
The first Seiken sold well enough to warrant the creation of a sequel, which was planned as Square’s debut title for Nintendo’s PlayStation CD-ROM system being developed in collaboration with Sony. But once again, the medium spoiled the message; when Nintendo pulled the rug out from under Sony’s feet and decided to axe the idea of a Super NES CD-ROM add-on altogether, SD2 was hastily repurposed as a standard SNES cartridge game. Presumably, this accounts for the rather noticeable game glitches which plague the game and its US counterpart, Secret of Mana. A different Seiken Densetsu appeared on the Gameboy in 1991. – [info from GAF?]