“I would like police to realise that if they fail to respond adequately, it could result in something similar to what happened to me,” Tomita told the Asahi newspaper.

In the months before the attack, Iwazaki sent Tomita books and a wristwatch as gifts, but she returned them. He responded by sending her more than 400 threatening Twitter messages, which Tomita reported to police.

Less than two weeks before the stabbing attack, she shared her safety concerns with police, who did not take any action because, according to Tomita, they regarded Iwazaki as posing no immediate threat to her well-being.

Two days before the concert, she again supplied police with details of her forthcoming performance, but they did not provide any additional security.

During Iwazaki’s trial, witnesses testified he shouted “you should die, die, die” as he stabbed her dozens of times in the chest, neck, arms and back, although his defence team claimed he had no intention of killing her.

He was sentenced to 14 years and six months in prison in February 2017.

The attack left Tomita hospitalised for four months and she remains partially blind in her left eye. She has problems eating and singing, and has not regained the full use of the fingers on one hand. She suffers post-traumatic stress disorder and will need further reconstructive surgery.

“When I see a person holding a pen, even if it is a friend or my doctor, I become really nervous because I fear I may be stabbed,” Tomita said. “It is difficult to return to what life was like before the incident.”

According to Tomita, police officers who interviewed her while she was still at hospital questioned if she had genuinely feared “she may be killed” when she first contacted police.

“I absolutely did,” Tomita said.

The conversation with officers is now central to her lawsuit against the police and her management, in which she is seeking damages worth 76 million yen (US$699,000).

Other Japanese stars have also been targeted by assailants. In 2014, two members of the girl band AKB48 were assaulted at a “handshake event”. Rina Kawaei, 19, and Anna Iriyama, 18, sustained broken bones and lacerations in the incident, as did a member of staff, before the assailant was subdued.

Satoru Umeta, 24, was later convicted of attacking the two women with a saw that had been adapted to hold box cutter blades. Umeta’s lawyer claimed his client was showing signs of schizophrenia. The attacker was found guilty and sentenced to six years in prison.

In October 2016, the management of Magical Girl Riripon, an idol who claims to be “eternally 16 years old”, cancelled events and moved her to a safe house after a fan implied on social media he wanted to rape her.

“Cases like this have become more common in recent years but so have stalking cases involving ordinary people,” said Makoto Watanabe, an associate professor of media and communications at Hokkaido Bunkyo University.

This attitude may be shifting, at least on the part of the authorities, who in December 2016 passed new laws to address online harassment.

Japan’s initial legal measures to combat the problem of stalking were introduced in 2000, but only specified loitering around named individuals, making repeated or silent phone calls or sending unsolicited messages by fax.

“Perhaps one reason we are seeing more stalking cases reported in the media is because the police are beginning to change their attitudes and we are seeing this problem treated more seriously,” Watanabe said. “But it will also take a change in attitudes among the public for things to change completely.”