Step into the Tokyo station underground, there is huge shopping areas.
You can meet some famous characters at “Tokyo Character Street”.
Domo-kun, Totoro, One piece or Naruto, of course Hello Kitty and rilakkuma, etc etc…
Do you know Nameko? They’re came from smart phone game, and now they’re becoming popular mushrooms.
Unfortunately this was limited pop-up shop, but I suppose you can find their goods at Tokyu Hands or Kiddy Land.