This story will run in Buffering, Vulture’s newsletter about the streaming industry. Head to vulture.com/buffering and subscribe today! Photo: Koyoharu Gotouge /Sony Pictures Releasing/Courtesy Everett Collection It’s been a lackluster summer at the box office, but last weekend proved a massive one for anime in theaters: Demon Slayer: Kimetsu no Yaiba — The Movie: Infinity Castle topped the charts with a $70 million opening, shattering several box-office records along the way . The thrice-