Yeah these people suck, too much time on their hands. But its kinda like how the KKK can technically march and gather legally in the states. It sucks, like... ALOT but they are allowed to do so. It's nothing new sadly though. These people exist in all countries and all we can do is counter them with a bigger, positive message.
What's up with the many anti Korea signs in the first video? Did I miss something recently or is this just the usual hate for Korea?
Most likely the later. Any time there is a slight spat between the nations, even ones they get over instantly these dudes try to make it like a big deal... then again, neither Japan or Korea do any real work to calm situations in their reporting. Both sides have a really condescending way or reporting events about each other. Will be happy go lucky reporting about vacations and celebs in each others nations, but soon as one of their boats gets too close to the other nations boat "irredeemable provocation of aggression!!!! I demand an apology!" -eyeroll- most normal citizens know this is all hot air, but it makes losers in the right wing all giddy for a few days.
In general though just speaking on Japan's right wingers, they range on all kinds of things they hate or "are conservative" about. Some are fine with Korea, but will hate like... Nigeria, or Malaysia, or Russia, or Australia, or literally insert any country or thing.