A 36-year-old man was arrested on suspicion of beating and shaking his girlfriend's 2-year-old boy to death.

On the 18th, the Kanagawa Prefectural Police Midori Police Station announced the arrest of Isamu Saito (36), a company employee from Tokaichiba-cho, Midori-ku, Yokohama City, on suspicion of assaulting a 2-year-old boy he was dating. ``There is no doubt that I punched him in the cheek, grabbed him by the shoulders, made him sit up, and shook him,'' he said. The boy was taken to the hospital in a state of cardiac arrest and later died.

According to the police, the suspect was arrested around 8pm on the 17th at Saito's home in Midori Ward, Yokohama City, for allegedly punching the eldest son (2) of a woman he was dating and shaking his body. The woman was out shopping and when she returned home, she noticed that her eldest son was exhausted and called 911.

The fire department rushed to the scene and called 110, saying there was a risk of abuse. When police arrived at Saito's home, the eldest son was in cardiac arrest, had multiple bruises on his face, and was bleeding from his nose.

According to police, Saito said, ``(The boy) was banging on the wall of the room and when I warned him, he pretended to be asleep, so I got angry.'' The suspect Saito and the woman met through SNS in September 2025, and on August 14 of this year, he brought the woman and her three children, including her eldest son, to her home in Yokohama from Yamaguchi Prefecture.

A man who lives in the neighborhood said he noticed something unusual when he heard sirens on the night of the 17th. ``I could hear the sounds of an AED (automated external defibrillator) being used and the voices of emergency personnel urging the mother to get into the ambulance,'' she recalled. A police car arrived shortly afterward and they realized it was an incident. "I've seen women and children before. It's painful," he said.

According to the Yokohama Northern Child Guidance Center, there has never been any consultation regarding abuse or other issues regarding this family, and they learned of the incident after receiving a report from prefectural police on the 17th. ``It's probably a temporary address, so I wasn't aware of it,'' he said.