I think nitoku is the best written character as he is a different type of guy compared to the rest of the main cast as he actually has a dream outside of fighting which cant currently achieve and he laments his abilities as a curse which is a cool dynamic.
Most underrated i would say is ohkubo as he seems to get slept on when he is actually a cool dude who has morals and a sense of camaraderie and strong fighter who just got unlucky in having to face the fang in the first round.