First of all, this is a seinen manga not shounen where the MC has to be the strongest one in everything though i believe kaneki is the one who will surpass arima, it just a matter of time. Besides that, kaneki is obviously holding back in this fight, he wanted to die and he doesn't want to kill arima since he was his mentor and sort of a father figure to him hence the reason why arima said " stop playing around " because he can sense that kaneki has no intent to fight him seriously, he was his mentor after all he should know better about kaneki's true abilities.One more thing, arima backstory and the reason why he is so OP has not been told yet through this story,is he really a human? But for him to has a spin-off story about his youth means that he is indeed an important character for this story. There are many hints that pointed him to be the OEK at this moment but even that is just an assumption.
I think he's the OEK too. I've thought that a while now and I'm so happy that I'm not the only one.
But.. I don't think it matters if Kaneki is holding back or not, Arima is just too powerfull for him right now.
I think it's impressive we will see how kaneki will beat him
First of all, I just want to say sorry for my rude comment, I just want to say anything in my mind about this manga.
I don't like the way sensei make Arima like TOOO OVER POWERED chara with no mistake.
Seeing a too over power chara just make me like 'yeah, he is the most powerful one, no one can beat him!'
Well if it's true then why don't make him the main chara since the first time Tokyo Ghoul?