I think what happened this chapters wasn't a huge "power up" of sorts for Hachi, I think this just furthers displays his massive potential. Again, the only reason that Hachi just made a massive passionate manga is because he had so much help. He's no where NEAR being able to do something like...
I really wanted Hachi to clobber Hoozuki right then and there. I adore when Eiji drops the signature explosive moment in all black. It's so impactful. Would've been even better with a massive punch right to the face.