On the seventh story of a Japanese tower block, an uncomfortable negotiation is underway. Behind a check-in desk, a hand extends through a heavy felt curtain and feels around for a credit card on the counter. Finding nothing, it quickly withdraws, and after a hidden, whispered kerfuffle, a receptionist emerges awkwardly into the windowless lobby. This is a love hotel, a kind of Japanese institution that rents out rooms by the hour to couples who want to be intimate somewhere other than home. Love hotels promise absolute discretion and aim…