A star-studded viral marketing stunt? This is “How It’s Done.” KPop Demon Hunters stars Rei Ami and Kevin Woo surprised fans with a concert from atop a double-decker bus in New York City on Saturday, August 23.

"KPop Demon Hunters" fans were in for a major surprise Saturday when cast members Rei Ami and Kevin Woo popped up in NYC and led a sing-along to "How It's Done," the intro song to the Netflix hit. The surprise performance was part of a series of "K-Pop Demon Hunters Golden Weekend" events.

The sing-along version of the hit animated film "KPop Demon Hunters" is officially streaming on Netflix. The film grossed $18 million at the box office.