And not shilling, go educate yourself. Vice News has some good coverage, split in 5 pieces, on it:
The most important things to note:
1) The Russian forces are not wearing insignias, or identifying themselves as Russian military. They either refuse to identify themselves at all, or identify themselves as being from the non-existent "Ukrainian Self Defense Force."
2) They Russian units are surrounding and/or capturing Ukrainian military installations. They are not moving to their bases, they are taking over Ukrainian bases. The Ukrainian commanders have been keeping things very cool, to avoid Russia being able to say they were provoked, so there hasn't been any violence, but it is a military attack on military targets, make no mistake.
3) Speaking of provocation, the Russian military has been trying it. They've been moving in and taking over Ukrainian bases, then withdrawing, only to do it again later. They are trying to goad the Ukrainian military in to firing on them.
4) Russia has been importing other non-governmental groups like Serbian Paramilitary forces to do, well who knows, but it isn't likely anything good.
So no, it is nothing like the US in Japan. Now if suddenly troops showed up in Maizuru and blocked off the military port there, troops wearing American uniforms, speaking English, armed with American weapons but wearing no insignias, no identifiers, and refusing to answer questions. If they blockaded the base, and then later went in and took it over, well ya, I'd be saying that the US was invading Japan and that it was clearly underhanded and illegit.
Having bases in a country doesn't mean free run to do as you please.