NOPE.
NOPENOPENOPE.
This guy cannot play the piano.
You cannot be as utterly moronic, as totally stupid, as pathetically f*cking dumb as this guy and still play the piano.
You have to use both hands in a fashion that, if you can do it, you are able to see things like, say... the fact that the people you flat MURDERED actually were not playing a chuunibiyo game for fun.
So... the rest, even the isekai, that I can believe.
This cat playing the piano?
Not a chance.