Now, after I started listening to K-pop too, I can say ONE OK ROCK would be a kind of Japanese FT Island but with more english and crazier songs. I mean, that is actual rock. Taka's voice is amazing. Again, he seems to be a Japanese Hongki. Seriously, I would love to hear these two sing a duet. It would be wicked! Anyway, there are songs I don't like from them. Yes, that exists. I guess at some point it became a little repetative. I mean the beat and the riffs and I believe they realized that too because their latest album (which came in 2011) was a bomb. It had all these insane guitar and Taka's voice sounded really good. Also they were more up beat and got me in a hyper mood.
This is one hell of a band and also, my favourite Japanese rock band. There's also Girugamesh and well, more, but ONE OK ROCK just has something, that sparkle a band needs to be succesful.