TOKYO, Sept 5 — Tokyo's Metropolitan Police Department on Thursday launched a police investigation into a series of incidents since July in the city’s Nakano Ward and its surrounding areas where men on bicycles grope women as they ride by, also known as "one-touch chikan” or one-touch molestation.

The term "one-touch chikan” refers to the crime of a single, often fleeting, act of molestation, according to a report published in The Japan Times today.

According to police sources, two incidents were reported on July 26 between 11.20pm and 11.30pm in Nakano’s Numabukuro district.

In both cases, a man on a bicycle allegedly groped a woman's breasts as he passed by.

A similar incident occurred on August 18 at around 12.10am in the ward’s Wakamiya district, involving a woman in her 20s.

Additional reports of such incidents have emerged from nearby areas, including Nerima Ward, during July and August.

On Thursday, Nakano Police Station announced the arrest of Daisuke Aose, a 24-year-old company employee from Wakamiya district.

Aose faces charges of indecent assault for an incident on July 20 at approximately 2am, where he allegedly groped a woman’s breasts while riding a bicycle in Nakano’s Chuo district.

During questioning, Aose admitted to having committed similar acts before, leading police to investigate his possible connection to the recent series of incidents.

"I’ve done this several other times,” he said in his admission.

Typically, in these cases, the perpetrator approaches from behind, gropes the victim while continuing to ride, and quickly flees the scene.

Most incidents have occurred along the Seibu Shinjuku railway line.

A senior investigator urged women walking alone at night to exercise extra caution, noting that such crimes often target victims from behind.