An Oahu grand jury Thursday returned an indictment charging a 36-year-old woman for allegedly sexually assaulting a bedridden 16-year-old exchange student multiple times at a boarding home she operates in Honolulu.

The grand jury charged Rika Shimizu with five counts of second-degree sexual assault and four counts of fourth-degree sexual assault.

Second-degree assault is a Class B felony that carries penalties of up to 10 years in prison. Fourth-degree assault is a misdemeanor that carries penalties of up to a year in jail.

Shimizu’s arraignment is expected to be scheduled in the coming days. Her bail is set at $600,000.

Shortly before the grand jury returned the indictment, she appeared in Family Court after prosecutors charged her with five counts of second-degree sexual assault. Shimizu did not speak and kept her head down throughout her initial court appearance.

According to a court document detailing the allegations, the victim reported to police that his dormitory supervisor, identified as Shimizu, sexually assaulted him at least 10 times from October to February.

Shimizu, of Japan, is the sole proprietor of ESL Hawaii, a boarding home for exchange students from Japan who are attending school in Honolulu. She is in Hawaii on a visa, according to deputy prosecutor Keith Seto.

The victim told police the first assault occurred in October. At the time, he was bedridden for several weeks due to a head injury. The court document said he was unable to go to the bathroom alone, prepare meals or change clothes.

During one late October night, police said, Shimizu entered his room where she sexually assaulted him.

The victim repeatedly told her to stop and that he was going to report her, according to the court document. Police said Shimizu told the boy that if he told anyone, she would tell everyone that he had raped her.

Shimizu also threatened to have him thrown out of the exchange student program and expelled from school, and implied his family would lose more than $20,000 that they had paid for him to be in the exchange program, according to court documents.

The victim said the last assault occurred in early February when Shimizu unlocked his room using her own key and sexually assaulted him, police said.

The victim’s attorney, Micky Yamatani, said the teen called his mother and told her of the assaults. She immediately contacted a family friend to take him out of the boarding house. The victim’s mother then flew to Hawaii from Japan.

The teen reported the assaults to police at the main Honolulu Police Department headquarters.

Police arrested Shimizu on Tuesday at a Kanewai Street residence, near the University of Hawaii at Manoa campus, on suspicion of 12 counts of first- degree sexual assault and 10 counts of third-degree sexual assault.

Yamatani described the assaults as “egregious.”

“He was an innocent resident of a so-called boarding house being run by this defendant who represented herself as the ‘boarding house mother’ who promised the victim a safe and healthy environment to study English and to experience the American schooling here in Hawaii,” Yamatani said in an emailed statement.

“This is a case of sheer betrayal of the trust this victim and his family endowed on this woman. Instead of providing a healthy and nurturing environment, the defendant engaged in sexual assaults of this minor child. We truly want to emphasize here that this crime involved a minor child,” she added.

Shimizu served as the victim’s guardian while he lived in the boarding house.

Yamatani said they are “sadly aware that there are those out there who have made the statements to the effect that (the) victim somehow enjoyed these sexual advances from someone 20 years (his) senior.

“To those who make such statements, we want to make it crystal clear that this victim is a young Japanese person who came to Hawaii to study English and to learn the American culture. He has been greatly betrayed by this woman, injured by this woman, been traumatized by this experience, and he looks forward to the day where our American justice system would set forth the truth and punish the person who harmed, hurt and injured him,” she said.