Pokémon Trading Card Game/Ishihara's House

This location is known as "??'s House" on the world map at the start of the game. The name will change to "Ishihara's House" once you have learned about Ishihara either from the Grass Club members while looking for Nikki or one of the several NPCs who mention Ishihara and cause him to appear in his house.

The NPCs who will tell you about Ishihara are a woman in the Rock Club lounge, a boy in the Science Club lounge, and a man in the lounge of the Fire Club. You can then head to Ishihara's House and talk to him. He won't want to trade any cards yet, but if you save and reset and talk to one of these NPCs they'll tell you that Ishihara is looking to trade cards. After each trade you'll have to save and reset, then talk to one of these NPCs to unlock the next trade.