Never mind that it's been open since 1933: it took until 2010 for Nihonbashi's Takashimaya department store to surrender to the inevitable and open a rooftop beer garden. With customers sitting at tables spaced well apart from each other, it lends itself to quiet enjoyment rather than raucous office parties (something that's compounded by the lack of all-you-can-drink deals). The Starlight Beer Garden still claims to be modelled on an Irish pub, though you'll have to make do with Bass Pale Ale and fish & chips in lieu of anything from the Emerald Isle.
Dates for summer 2018 are yet to be determined – keep checking back later in spring.