A 13-year-old girl was suffocated by her father and a monk who were trying to expel an "evil spirit".
The girl died after she was strapped down and doused with water, Japanese police and media reports said yesterday.
The two men, 56-year-old monk Kazuaki Kinoshita and the girl's 50-year-old father Atsushi Maishigi, were arrested on charges of inflicting injury resulting in the death of Tomomi Maishigi in Kumamoto in the country's south.
"The two are suspected of having conspired in what they call 'waterfall service'... They allegedly strapped the victim to a chair with belts and doused her face with water," on the night of August 27, a local police spokesman said.
The girl was confirmed dead early the next day when her mother called an ambulance after the victim fell unconscious.
"The cause of death is suffocation," the police official said.
News reports said the two men poured water over her as an "exorcism" with the father holding the girl down while the monk chanted sutras.
Reports said the the girl's parents had turned to the monk after the youngster had suffered several years of mental and physical ill health that doctors had not been able to resolve.
The monk, who belongs to a religious group deriving from a Buddhist sect, said that the girl was possessed by an evil spirit, the private network TBS said.
Her parents had taken her to one of the group's facilities equipped with a water pump and made her go through the dousing practice about 100 times before, the broadcaster said.
The pump pulls water from underground and draws it to a height of 2.5 metres, from where it falls on the person sitting below, TBS said.