[ She's...still in the same house but of course Nanami has to answer this one immediately, instead of hunting down Saionji.

This is a gaming question, her time has come. ]

In the game, it's a Pokémon that there is only one of...and a master ball is useful in catching them, since that one has the best capture rate. There's normally stories about them in the lore, too, I think.

The ones from the game are...Zapdos, Articuno, Moltres, Mew, and Mewtwo. But, there are ones here, too. ...I think.