Pokémon X & Y may have sold great guns, but it doesn't seem to have the staying power of previous incarnation Black & White.
According to Media Create data harvested by Siliconera, Japanese sales of Pokémon X & Y dropped to 473,000 in its second week, a decrease of 75%.
The original Pokémon Black & White, saw sales drop by 70% during its second week. That 5% difference may not seem substantial, but the 2010 DS title also had high first week sales.
The 3DS's smaller install base - less than half that of the DS in 2010 - is likely a contributing factor to the reduced sales. Certainly Nintendo seems happy with the RPG's figures; it shifted 4 million units worldwide in its first two days and drove the 3DS up the US hardware charts.