I'm trying to figure out what the rarest Japanese Playstation games are. The Online Rarity Guide says it's Netz Toyota Racing, but even if it was the rarest, it's hardly the most valuable. (It seems to be valued around 1500 Yen)

If rarity equals most money and least information, this one must be it:
http://page10.auctions.yahoo.co.jp/jp/auction/m35976045

It's "Bogus Fropon-kun P" and the subtitle reads, "Famitsu takeover version." Aside from this auction, I could find next to nothing about it on the internet. It isn't in the rarity guide either. The above auction link lists it as "Propon-kun" for reasons I don't know. It appears to be a promo game for Famitsu. Has anyone seen or played it and can clarify things?