Japanese prosecutors sought Monday an 18-year prison term for the stepfather of a 5-year-old girl over the assault and neglect that led to her death, in a high-profile child abuse case.

Yudai Funato, 34, is accused of causing the death of his stepdaughter Yua from sepsis in March last year. The defendant allegedly restricted her food intake from around late January last year, beat her up and did not seek medical care despite her weakened state while at their home in Tokyo's Meguro Ward.

"The defendant led the severe abuse. He made the girl suffer from starvation by limiting food. He bullied the victim to such an extent that she had nowhere to escape," a prosecutor said during closing arguments at the Tokyo District Court. "The crime's maliciousness is severe beyond comparison."

"We have to think about the agony and chagrin of a child who was deprived of her future by her parents," the prosecutor said.

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The stepfather has admitted to most of the charges. The defense argued that a nine-year term for him is appropriate. The court will hand down its ruling on Oct. 15.

Wearing a dark suit, the defendant looked nervous with a tight expression, clenching his fists on his lap as prosecutors made their argument. "I'm really sorry," a crying Funato said in his final statement while standing, although Presiding Judge Minoru Morishita asked him if he wanted to sit down.

He closed his eyes, expressionless as he heard the prosecutors' recommended sentence.

The prosecutors have alleged Funato gave the girl tasks, including telling her to wake up at 4 a.m., and shouted at her and grew violent when she did not obey.

They also claim he failed to take her to doctors despite Yua throwing up repeatedly from the end of February last year, as he feared the abuse would be discovered. He "ran away so as not to confront the reality" out of "self-protection," the prosecutor said.

Yua left behind written messages such as "Please forgive me" on a sheet of paper, which prosecutors regarded as pleas for her mistreatment to stop.

The girl weighed about 12 kilograms when she died, far less than the 20-kg average for her age, and had 170 injuries, according to the prosecutors.

Funato's defense team has challenged the prosecutors' timeline, arguing the defendant realized the child's life was in danger only a day before her death on March 2, 2018.

The defense team added that Funato, who is also charged with marijuana possession, did not completely neglect Yua as he sometimes fed her bananas, and "tried to become her father."

"My disciplining was unsuccessful, and I started assaulting her as my anger grew. I am responsible for everything," he said Friday during questioning by his defense counsel in a lay judge trial.

He also defended himself at times that day by saying that his memory was vague, when quizzed by prosecutors about details of the sequence of events.

Yua's 27-year-old mother Yuri, now divorced from Funato, received an eight-year prison sentence in September for parental neglect resulting in her death.

The ruling against her recognized she suffered psychological abuse by Funato, but added she "was aware of the violence (against Yua) and allowed it." She has appealed the court decision.

At Funato's trial on Thursday, which the mother attended as a prosecutors' witness, she said, "There are people who can help me now. I don't want him to approach my child."

The couple have a boy, born in 2016, who is said to have had no food limits, unlike Yua. The mother will raise him.

Yua had twice been taken into protective custody by a child welfare center in Kagawa Prefecture, western Japan. Another center in Tokyo tried to check on her in February last year, but her mother refused access.

The high-profile abuse case has prompted Japan to revise laws, banning parents and guardians from physically punishing children and strengthening the ability of child welfare centers to intervene in cases where abuse is suspected.