What would Japanese people do if I walk around Tokyo in a Darth Vader suit?

Question:

And stand on top of elevators and tell people "may the force be with you" when they come up, and run around in traffic (not blocking traffic).

Will I get arrested?

If I enter a nude bath filled with yakuza members and wearing only darth vader helmet, will they beat and torture me?

Answer:

I guess people would try to ignore.
Japanese police officers are very friendly to silly people. They know their budget is not to play with you.
You should remember most of them even don't understand "may the force be with you"
Yakuza members, in bath, should be busy enough to polish up their tattoo, with only four fingers on the left hand. No time to pay attention to Darth Vader.