A couple in Ibaraki, Osaka Prefecture, have been arrested on suspicion of starving their 3-year-old daughter to death.
The stepfather, 22, a carpenter, and the 19-year-old mother have denied the allegations.
The daughter was only around half the average weight for a child her age when she died, the police said Thursday.
An autopsy found onion skins, aluminum foil and wax in the girl's intestines, apparently eaten in an attempt to relieve her hunger pangs.
The police suspect the couple failed to feed the girl sufficiently starting around February and allowed her to die on June 15. She weighed 8 kg at the time of her death. The autopsy showed she died of malnutrition.
The girl had earlier been hospitalized for about seven months to treat a congenital disease that results in slower-than-normal physical development and muscle weakness.
Meanwhile, in Tsubame, Niigata Prefecture, a 24-year-old woman was arrested on suspicion of killing her 3-year-old daughter by throwing her off a bridge into a river.
Ayumi Sato, an office worker, allegedly dropped her daughter, Miyu, from a bridge in Tsubame on Wednesday night. She has admitted to the charges, police said.
Sato went to a hospital on Thursday morning where her daughter had an appointment booked and told a staff member that the girl "had disappeared," police said.
The hospital notified the police, who began a search of the area. They found the girl's body floating in the river at around 3 p.m. on Thursday.