You don’t have to get up because another person gets on, for priority seats they are reserved for those with “special needs” I.e. the elderly or disabled. But it’s common courtesy everywhere to offer your seat to an older/disabled/pregnant passenger.

People should also absolutely be judged for disturbing the peace if you want to talk to your friend on the train you talk in a quiet respectful volume there is no need to talk loud enough everyone around you can hear it.

The Japanese just generally have a respect for rules and for not negatively affecting other people