Japan’s harsh treatment of its female celebrities has again come under scrutiny following outcry over the music industry’s handling of an alleged assault on a member of a popular girl band.

Social media users and TV commentators have joined the barrage of criticism targeting AKS, a music management agency, after Maho Yamaguchi, a singer with NGT48, went public this month with allegations she had been assaulted by two obsessive fans at the end of last year.

Yamaguchi, 23, said on Twitter that AKS had failed to help her after the assault, which had left her deeply traumatised. At the time of her tweet, the agency representing NGT48 – a sister group to the hugely popular girl band AKB48 – had not commented on the incident.

The furore intensified when Yamaguchi bowed deeply and apologised to fans for “causing trouble” – making fans worry by speaking out about her assault – during a concert earlier this month. Many questioned why she felt she should apologise while her industry handlers remained silent.

Her fans responded with a petition calling for NGT48’s manager to resign that was signed by more than 53,000 people.

Yamaguchi’s case has highlighted the poor treatment of young women and girls by Japan’s pop industry, particularly the insistence that they appear morally unimpeachable.

Performers are subject to strict rules imposed by their management agencies, including, in many cases, a ban on having boyfriends to maintain the impression among their largely male – and, on occasion, dangerously obsessive – fan base that they are romantically available.

In 2013, Minami Minegishi, then a 20-year-old member of AKB48, shaved her head – a traditional act of contrition in Japan – and issued a tearful apology after breaking her group’s strict dating ban to spend a night with her boyfriend.

In a comprehensive account of the latest incident, Twitter user @katbeee said Yamaguchi’s experience highlighted the widespread mistreatment of women in Japan’s idol industry.

“To the West, all this “idol drama” can easily come off as “WACKY JAPAN!” nonsense — but these incidents and lack of regulation in the idol industry are as serious as the abuses committed in the Western entertainment industry,” she said, adding that the industry was rife with “power harassment, sexual exploitation, emotional and psychological abuse and overwork”.

AKS eventually apologised for its handling of the issue, claiming it had remained silent throughout Yamaguchi’s ordeal to allow the police to investigate. A spokesman said the firm had replaced the manager of the theatre in Niigata, northern Japan, regularly used by NGT48, adding that it would step up security around members of the group.

The firm also admitted that a fellow NGT48 member had given the men Yamaguchi’s address and told them when she might return home.

The two men suspected of grabbing Yamaguchi’s face and pinning her to the ground as she was entering her home in Niigata reportedly told police they had simply wanted to talk to her and were released without charge.

NGT48 has cancelled three upcoming concerts in which Yamaguchi was to perform, according to Japanese media.