A Japanese court on Friday sentenced a 25-year-old man to 10 years in prison for scalding his girlfriend's toddler son to death with hot shower water at their apartment in Osaka Prefecture in August 2021.

Prosecutors had charged Takumi Matsubara with murder and assault, seeking 18 years, but the Osaka District Court found his actions only amounted to bodily injury resulting in death, noting that he had not intended to kill 3-year-old Orito Niimura.

The court convicted Matsubara of assault, recognizing that he hit the boy's head with a cushion.

Presiding Judge Hirotoshi Sakaguchi said the child suffered burns to more than 90 percent of his body, and that Matsubara left him in a running shower with the temperature set as high as 75 C.

But Sakaguchi deemed the evidence put forward by prosecutors about Matsubara's motive insufficient, establishing that it could not be said Matsubara was aware of the risk to the young child's life.

His legal team argued that Matsubara, who was having difficulty potty training the boy, wanted to punish him by shutting him in the shower room with the water running.

"(The child) must have cried and screamed in considerable agony. This was nothing other than cruelty," Sakaguchi said.

The boy's mother was not at home in the city of Settsu at the time of the incident.

She had consulted the local government in May of that year and alleged her boyfriend had been abusive to the child, but the city's consultation center concluded that the situation at the time did not warrant implementing protective measures.