Photo/Illutration Maho Yamaguchi tells fans that she is leaving the idol group NGT48 at a concert held in Niigata on April 21. ((c) AKS)

NIIGATA--A member of local idol group NGT48 is leaving the troupe after accusing management of covering up an assault against her by men she said were in personal relationships with other group members.

“I will graduate from NGT48,” Maho Yamaguchi, 23, told fans during an encore of a concert held at NGT48 Theater in Niigata on the night of April 21.

Two other members, Rena Hasegawa and Riko Sugahara, both 18 and close to Yamaguchi, also announced they will leave NGT48. The three will hold a “graduation concert” on May 18.

The scandal started on Jan. 9, when Yamaguchi said on her Twitter account that she was assaulted by two men on Dec. 8 last year.

She explained that they grabbed her face and shoved her down at the door when she came home.

Niigata prefectural police on Dec. 9 arrested two men in their 20s, who were NGT48 fans, on suspicion of assault.

Later in the month, the Niigata District Public Prosecutors Office decided not to indict the suspects without revealing the reason.

Yamaguchi, via Twitter, said multiple members of the idol group had personal relationships with the suspects and tipped them off about where she lived and the time she would arrive home.

She also said AKS Co., the company that manages NGT48, showed indifference when she reported the incident, and that AKS officials tried to sweep the potential scandal under the rug.

In fact, at a Jan. 10 group concert, Yamaguchi ended up apologizing, saying, “I am very sorry to have caused much trouble.”

Her April 21 concert was her first public appearance with the group since that apology, 101 days ago.

But Yamaguchi never stopped expressing her mistrust and frustration over how AKS handled the case.

AKS held a news conference on March 22 to explain the incident, but without Yamaguchi’s presence.

In the middle of the news conference, she tweeted, “Why do they lie about everything?”

Before the news conference, an independent commission investigated the incident and found that Yamaguchi got into a scuffle with the men. But it concluded that it found no involvement by any group member in the attack.

Yamaguchi helped to found the idol group in 2015 as a sister group of AKB48.

East Japan Railway Co. (JR East), the Niigata prefectural government and Niigata municipal government were among those who have used the group for TV commercials and image characters.

But since the scandal rocked the fan base of NGT48, sponsors have terminated their contracts with the group or deferred decisions on contract renewals.

Local TV and radio stations have also discontinued the group’s namesake programs.

Facing difficulty surviving, NGT48 has announced it will make a fresh start.