A series of incidents involving cyclists groping women in Tokyo’s Nakano Ward and surrounding areas has sparked a police investigation, the Metropolitan Police Department said Thursday.

There has been an increase since July of men on bicycles touching women as they ride by, with investigators dubbing the crime “one-touch chikan,” or one-touch molestation.

According to police sources, two incidents occurred on the streets of Nakano’s Numabukuro district on July 26 between 11:20 p.m. and 11:30 p.m. In both cases, a man on a bicycle allegedly groped a woman’s breasts as he rode past.

A similar incident was reported on Aug. 18 at around 12:10 a.m., this time in the ward's Wakamiya district, involving a woman in her 20s.

Several other incidents have been reported in nearby areas, including Nerima Ward, in July and August, police said.

The Nakano Police Station announced on Thursday the arrest of Daisuke Aose, a 24-year-old company employee from Wakamiya district, on suspicion of indecent assault. The specific charge against Aose stems from an incident on July 20 at around 2 a.m., when he allegedly grabbed the breasts of a woman in her 20s while he was riding a bicycle on a street in Nakano’s Chuo district.

During questioning, Aose made an admission, saying, “I’ve done this several other times,” prompting police to investigate his connection to the series of recent incidents.

In most of these one-touch cases, the perpetrator approaches from behind, gropes the victim while continuing to ride, and flees the scene. The incidents have predominantly occurred along the Seibu Shinjuku railway line.

"Women walking alone at night are often targeted from behind, so we urge caution," a senior investigator warned.

Translated by The Japan Times