NAGOYA - A mother was on Tuesday (Sept 17) jailed for eight years for parental neglect, in a high-profile fatal child abuse case that has led Japan to enact stiffer laws including a ban on corporal punishment on children.

Yuri Funato, 27, had pleaded guilty to turning a blind eye to the abuse meted out by her ex-husband Yudai Funato, 34, on her five-year-old daughter Yua.

In the heart-rending case, the child ostensibly blamed herself for being at the receiving end of abuse from her stepfather. She begged for her parents' approval in journal entries, such as one which read: "Please, please, please forgive me. I will make sure I can do more things tomorrow than today without daddy and mummy having to tell me what to do."

Her journal entries triggered such a huge outcry that Prime Minister Shinzo Abe addressed the case in Parliament.

Yua died in March last year, just 18 days shy of her sixth birthday, of blood poisoning after developing pneumonia, malnourished and left in a room without a heater in winter.

She was just 12.2kg, or the healthy weight of a two-year-old girl.

Yuri, who has divorced Yudai, bore him a son in November 2016. Yudai's abuse of Yua started around the same time.

His trial will begin on Oct 1.

Japan's well-documented struggles to raise its birth rate have coincided with a startling increase in child abuse cases. Government figures last month showed that the number of cases reported to childcare authorities nationwide surged to a record 159,850 in the year ending March 2019.

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The increase of nearly 20 per cent from a year ago was officially attributed to heightened awareness of child abuse among the public.

Yua's case had fallen in between bureaucratic cracks after her family moved from Kagawa prefecture to Tokyo's Meguro ward in January last year, prompting new laws to give child welfare workers more powers to intervene.

Yuri was found to be complicit in causing Yua's death by, among other things, failing to alert the authorities or her parents of Yudai's abuse - meted in the name of discipline - and preventing child welfare workers from seeing Yua, given the bruises on her face.

After the family moved to Tokyo, Yua was often locked at home and starved even as the couple doted on their boy.

Prosecutors said she lost more than 4kg in two months, from being fed just a couple of servings of soup a day. While they sought an 11-year term, defence lawyers argued for five years as Yuri herself had been a powerless victim of "relentless psychological domestic abuse".

"I was scared he would try to take revenge on me, and so I could not report the abuse to the police," Yuri said during the trial.

Defence lawyers added that Yuri was made to obey her husband if she did not want Yua to be harmed.

But prosecutors argued that notwithstanding this, she had "failed to do a parent's bare minimum", noting that she failed to take Yua to hospital even after the child began vomiting in the week before she died.

A psychiatrist who was a defence witness said the case was a result of a tempest of factors. "It's a typical horrifying example of what happens when domestic violence and child abuse occur together."

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Yuri told the court that she pined for her daughter: "I blame myself and will never forgive myself. I'm mortified and full of regret."

"I want to die. I want to go to a place where I can be with Yua," she said. "I will receive punishment seriously (for) having left Yua's mind and body in tatters."