However, it's essential to differentiate between sensationalized stories or urban legends and factual, verified information. Japan does have its share of stories about youth groups and subcultures that interact with the train system in unauthorized or non-standard ways, but these are typically not widely publicized.
A very famous JAV actress named (yes, same name reversed) starred in a popular series called “Train Groping Special – 10 Actors vs 1 Actress” (code: DANDY-xxx). Search for “Nagi Hikaru train” on free sites yields many results, often miscategorized as “Nagi Hikaru gang train.” video title a japenese hikaru nagi train gang free