Ok, I know I have written about Hayato several times in the past, however I really, really believe that he's rather underpowered. He is, in essence, a fast-paced mobbing warrior. His 1v1 ability, Shinsoku, seems rather underwhelming, even with Hypers believed and even a good bit of
Maplestory M Mesos. This endangers him at worst, frees him greatly at least for most major directors (Empress, Tough Magnus, to mention two ).
Aside from that, I think that Hayato, for it's current underpowered standing, is rather tough to buff with out getting overpowered. It is already kind of a bully class early to mid match (Lv. 30-130) in terms KSing possible because of his mobbing abilities, and his blisteringly fast strikes.
If you were to adjust the damage%'s of his Sanrenzan, or even add additional attack lines, then it gets him overpowered. Perhaps if Shinsoku had a higher% damage per line, it might help matters, but I'd suggest adding a bind of some sort to his kit.
Now, abilities aside, I also believe that there is an even greater reason he does not get
buy Maple M Mesos as much love from players: his command. Granted, he's 60% mastery from the very start, but that would be it. Other courses get 80% mastery, maintaining their damage comparatively steady. Hayato? His damage jumps about as much as he does. There is also the issue of his attack multiplier (which is very tough to adapt in a means that's balanced).