A 7-year-old boy was injured Saturday when an unidentified man assaulted him with a paper cutter in Sekijo, Ibaraki Prefecture.
Police said Reito Kikuchi sustained several cuts to his chest, while his 4-year-old brother, Etsufumi, was hit on the face when the man attacked Reito.
Police launched a search for the attacker, who fled the scene.
A mark on Reito's neck suggests the man also tried to strangle him, according to the police.
The man attacked the boys apparently while they were playing outside their home, the police said. The incident took place while their parents and a grandfather who lives in the house were away.
The two children were taken to a hospital. The cuts to the older boy are not life-threatening, police said.