Lee Kwang Jae, the designer of the shirt, issued a statement after learning BTS had canceled their trip to Japan.
The comments included, "The dropping of the atomic bombs led to the end of war, then liberation"; "It can not be swept aside simply by saying, "We wore it without knowing the meaning"; and, "I feel sad and pained that their chance to perform on the program is gone". The problem is not the relation between Japan and Korea.
Universal Music said it will continue to support BTS but confirmed their appearance on the live music show Music Station was cancelled.
"We have seen news that a T-shirt worn by one of the members has set off a furore. After asking their record company about this, we made the decision to postpone their appearance on our Nov 9 show", TV Asahi said in a statement.
The shirt is still available for purchase online.
The shirt features the words "Patriotism Our History Liberation Korea" repeated next to an image of an atomic bomb's mushroom cloud (though it's hard to tell, it appears to be the Nagasaki explosion) and a picture of Koreans being liberated from Japanese colonialism.
Japan became the first nation to suffer an atomic bombing on 9 August 1945, at Hiroshima.
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Both South Korea and Japan are particularly sensitive when it comes to the legacy of World War II.
There are conflicting reports as to when exactly Jimin wore the shirt.
BTS member Jimin reportedly wore the shirt past year, on August 15, when Koreans celebrate the end of Japanese occupation in 1945.
Photos of Jimin in the shirt started to gain traction on social media in early November.
Claiming that the T-shirt instigated anti-Japanese sentiment, the media outlet even described the group as "anti-Japanese".
Now, after BTS's incident with "Music Station", these netizens are more aggravated than ever regarding IZ*ONE's ongoing, active promotions in Korea.
"A-bomb t-shirt" was one of the top trending topics on Twitter Friday morning.
"What's so wrong about Koreans commemorating National Liberation Day?" said another Korean user on Twitter.