It's all part of the healing process. Similar to blood stains being removed in anime when the character is healed.

Or Hulk's superpants.

I'm pretty sure they don't have a model for Wolverine's or Hulk's  groin.

Shouldn't the conclusion go both ways? I mean, if the Muramasa can cut through Adamantium due to it's vibrations, shouldn't Adamantium also cut trough Muramasa due to it's vibrations? If so, that would be 6 blades against one which can destroy each other, so Muramasa shouldn't stand a chance.

Also, where does Raiden know he has to destroy Wolverine's head in the end?

Who knows? Maybe one of their artists has a special drawing of one of them, secretly kept on his possession, that he goes back to from time to time for inspiration.

He'd probably destroy it because he's crazy as Jack The Ripper. And Adamantium isn't Vibranium. It doesn't vibrate that much.

Knowing the internet, there;s already something like that.

 The head is kind of a pretty obvious thing to target for a killing blow, especially when nothing else. You'd might as well ask why a sniper would go for a headshot. It's where the brain is, so that's the best way to guauntee a kill, especially when hitting every other vital area hasn't worked.

So, I can't watch the video, at work. But are they claiming that Raiden can cut Wolverine's Adamantium? Also, are they talking about movie Wolverine or comics Wolverine? They are completely different people?

Silver Samurai who has the mutant power to charge objects with tachyon energy, specifically his sword allowing it to cut through virtually anything cannot cut through Wolverine's bones. There are also a few Muramasa blades in the MU none of which can cut Wolverine's bones and can withstand his own Adamantium blades.

Do they mention any of this?

This is without the fact that Wolverine is as good of a fighter as any martial artist in the Marvel Universe with the exception of Shang Chi.

Well aparently there's somebody called Misty Knight who has an arm made of Antarctic Vibranium. This anti metal emanates vibrations which weaken its targets molecular bonds, exactly like Raiden's high frequency blade. Then they showed her liquefying a sword made of adamantium. And they aknowledged that Wolverine was a better fighter. They talked about comics Wolverine.