"As a senior member of the group, it is my responsibility to be a role model for younger members," she said, before ending the four-minute mea culpa with a deep, lingering bow.
The most striking thing about her apology, however, was her appearance. She had shaved her head, a traditional act of contrition inJapan, but perhaps a step too far for a 20-year-old woman whose "crime" was to have found herself a boyfriend – 19-year-old Alan Shirahama, a dancer in a boyband.
Minegishi explained she had decided to cut off her long hair immediately after seeing her photograph, her face hidden behind a surgical mask and a baseball cap, in the weekly tabloid Shukan Bunshun on Thursday.
Her dramatic gesture underlined the strict rules to which Japan's young pop stars must adhere to project an image of unimpeachable morals.
In the YouTube video, which has been viewed more than 3m times, Minegishi said the assignation has been "thoughtless and immature".
"If it is possible, I wish from the bottom of my heart to stay in the band," she said. "Everything I did is entirely my fault. I am so sorry.
"I don't believe just doing this means I can be forgiven for what I did, but the first thing I thought was that I don't want to quit AKB48."
AKB48's management agency demoted her to "trainee level" starting on Friday, according to the band's official blog.