It's not all cheesy Sky Tree swag at this mall under the tower (though you can get 634m-long rolls of Sky Tree toilet paper). Shops on the 4th floor offer a better-than-usual selection of Japanesey souvenirs, including pretty trinkets made from kimono fabric and quirky fashion items.
Tower Knives is here, as is Sumida City Point specialising in products made by the craft businesses of Sumida ward. There are also branches of food model shop Ganso Shokuhin Sample-ya, chopstick specialist Natsuno, and Pokémon Center Mega Tokyo.