I'm not that familiar with japanese trains tbh, but from what I've read they seem to have some pretty neat ones. Shinkansen looks fucking futuristic.
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When it comes to high speed train my heart has always been with the German ICE-trains though, the third generation also tops over 300km/h but the older ones are my favorites. Lots to do with them being featured in old Märklin-cataloges and all.
But heavy as fuck cargo trains are still cooler, there is something special about multiples of really strong locos crawling up through the mountains with a trail of cars that appears to never end after them.