Sounds like one of countless Space Invaders clones. I'm willing to bet that since this machine has Japanese characters on it it's probably overseas only but it's still not worth much since this type of bootleg are a dime a dozen. It's RARE, in that you're probably not ever going to see that particular Japanese machine again for sale, but it's not valuable because you'll come across a ton of similar machines over any given span of time. It is possibly a prototype (I know Sega made several odd Space Invaders knock-offs, perhaps this particular one had its name changed before release) but to your average collector, a normal, common original Space Invaders machine is worth more. Also, many Japanese titles, especially clones, aren't documented on the english side of the web, so it may be common over there, who knows. It's worth submitting it to KLOV for listing regardless.You may get a decent sum from a collector of variations/bootlegs but those are one in a million.
Still, I dig weird knock-off machines, especially of the foreign variety. Any chance you could post some pics?