Akasaka's restaurants are an eclectic mix. Cheek-by-jowl with the raucous pubs, ramen counters and Korean kimchee kitchens, you find inscrutable anonymous facades, many of them exclusive ryōtei (traditional restaurants) reserved for politicians and captains of industry.
Kagura does not operate at that rarefied level. But even so, it gives little away from the outside save for the kanji characters of its name illuminated on the wall, and a concise menu (also in Japanese) by the imposing dark-wood door.
It's certainly not the sort of place you'd enter on a whim. And even if you did, you'd be turned away, as it's invariably full. If you like the intricacy of high-end Japanese cuisine but in a relaxed setting, then it's well worth picking up the phone to make that booking.