yosou no naname ue
obliquely above one’s expectation
(something is done) in a completely unexpected and idiosyncratic way
It’s often used as 予想の斜め上を行く. You can also use the word 想像 (“imagination”) instead of 予想 (“expectation”). It is a slang word and often used on the internet.
The movie became a big hit because of its very unique and completely unexpected storyline.
I sent a LINE message to my friend and got a completely unexpected reply