Kakigōri (shaved ice) is a huge thing in Japanese summers, and this shop is owned by a long-standing ice company so you know the main ingredient is top notch. Toppings span classic (strawberry milk), Japanese (kinako, soy-bean powder) and a 'literary-creation menu' including matcha and mascarpone or hoji-cha (roasted tea) mont blanc. It's hard to get more refreshing.
Look for the post-industrial space by the Docomo store.