The band was revving up the crowd at the private, beachside concert, the lead singer punctuating musical notes with pumping fists - "We. Are. Seventeen!" - unaware of the approaching danger.
As he walked across the stage Saturday night, a tsunami wave hit the shore of Tanjung Lesung beach on the western tip of Java, knocking the stage out from under the band and bringing the concert to a sudden and tragic end.
In a video recorded by someone standing several yards away, the stage - with the band members on it - briefly floats as the water hits and then is washed away. Band members disappear underwater. People in the audience scream as they try to flee the approaching seawater and music equipment. Then the video abruptly ends.
According to Reuters, four people connected to the band were killed: bassist M. Awal "Bani" Purbani, road manager Oki Wijaya, guitarist Herman Sikumbang and crew member Ujang.
The band's drummer was still missing, as well as the lead singer's wife.
One crew member, identified by Channel News Asia only by the first name Zack, said he survived by holding on to part of the collapsed stage.
"Underwater, I could only pray 'Jesus Christ, help!'," Zack said of his struggle in the water. "In the final seconds, I almost ran out of breath."
The private concert by Seventeen was part of an end-of-year celebration for Perusahaan Listrik Negara, the country's electricity utility, according to Channel News Asia. Twenty-nine people who attended were killed by the tsunami waves.
On Sunday, Seventeen's lead singer, Riefan Fajarsyah, posted a tearful video on Instagram, apparently still wearing the shirt in which he had performed the night before.
"Andi, Herman and Ujang have not been found, please pray for them," he said as he wiped away tears. "Please pray also that my wife will be found soon. Please pray also for Bani and Oki (who passed away)."
The washed-away concert was just one of the dramatic stories that emerged after tsunami waves struck Indonesia's Sunda Strait without warning, killing at least 222.
By Sunday night, Indonesian government officials said more than 843 people were injured and 28 were missing.
Indonesian officials postulated that a volcanic eruption caused undersea landslides that generated the massive waves, Stanley Widianto reported for The Washington Post.
But the volcanic event did not create the tremors that typically put coastal residents on tsunami watch - and the government never issued a tsunami warning.