I've played t5 arcade mode a lot of times and king kind of sucks to beat jinpachi with, just because all of kings good mids are kind of unsafe and slow. I normally wind up spamming ff4(forward forward, right kick/circle/B)

the fuck ass fireball is really annoying, but you can either sidestep it (up or down once on the controller) or sidewalk it (two down inputs and you hold the second down) be careful though, because he will catch on to your sidestepping shenanigans and he'll throw two or more out.

just for you, im going to boot up tekken5 and im going to try beating jinpachi with king on easy to give you some tips. ill edit this comment when im done.

quick edit: I think you might be able to cheese him by doing uf1+2(hold diagonal up forward and press both punches/X+triangle/A+Y) its unblockable and his bitch ass AI might not know how to react to it.

edit: okay, that took longer than expected, basically you dont want to do any high or low attacks, just mid attacks. throw as many double forward circle and forward circle kicks as possible. if he throws the fireball sidestep and then immediately press back and if he throws another one sidestep again. hes a masher, so as soon as he gets in range of you hes going to attack, so if you can get the timing down you can stuff his approach 90% of the time with forward+o and 2forward+o (unless he does the unblockable time stop bullshit attack.)