While calling for President Yoon Suk Yeol’s removal, tens of thousands of South Korean protesters have danced to traditional percussion, sung a pop genre called trot and blasted “Whiplash,” a hit by the girl group Aespa.

They’ve also left rallies with the melody of “Feliz Navidad” stuck in their heads. The adaptation’s repeated opening verse: “Impeachment is the answer.”

The day after Mr. Yoon’s short-lived declaration of martial law last week, the protest anthem’s creator, Baek Jae Gil, performed it for thousands outside the National Assembly in Seoul. A recording has received nine million views on X, and the song has spread on TikTok, Instagram and YouTube. On the Chinese app WeChat, it has been translated into Chinese, he said.

“If Yoon Suk Yeol gets lost, it’s a Merry Christmas,” the crowd sang along to the tune of the 1970 Christmas classic.

Mr. Baek, 52, a professional musician known as Baekja, has been protesting for decades. He has seen demonstrations become more peaceful and the mood lighten since his first rally in 1989. That was during a brutally suppressed teachers movement that led to the formation of a national union.