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” fever is gripping New York, with the stars of the wildly popular animated Netflix film lighting up the Empire State Building on Friday. The movie, which premiered on Netflix in June, quickly became a blockbuster hit around the world, with the streaming giant now releasing a sing-along version in Big Apple theaters this weekend.

"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.