Crowding, confrontations and full-on attacks. Japan's many train fans are mostly mild-mannered enthusiasts passionate about the country's famed rail system, but a small group is gaining surprising notoriety.

Japan's railway system has long inspired envy around the world, with its famed punctuality, cutting-edge technology and meticulous timetables. So it's no surprise that the country is home to a diverse landscape of train buffs, from those who enjoy poring over timetables to others who adore and even record the rumbling sound of passing trains.