When the Straw Hats landed on the island of Punk Hazard, they came across a strange pair of moving legs. After further investigation, they found the head and torso, as well. The man explained that his name was Kin'emon, and that he was a super-powerful samurai who had to rescue his samurai friend as well as his son Momonosuke.
What I first think: Huh, I don't remember that! Is that fanfiction?
Alas, no. Kin'emon is a unique character, not in terms of personality, but in popularity. When he was introduced, Oda most likely intended to make his story a major part of the Doflamingo/Kaido arc. However, Kinemon faced a slight problem: EVERY NEW THING INTRODUCED IN THE PUNK HAZARD/DRESSROSA ARC OVERSHADOWS HIM.
This brings to light the question "Is Kinemon a failed character?" While it is he that starts the Straw Hats' adventure on that island, you kind of forget about him as soon as Caesar, Smoker, Law, Vergo, Monet, and even the Yeti Cool Brothers and the dreaded giant kids are introduced. You start to remember him somewhat after Momo is introduced, but ultimately Kinemon is relegated to "minor character" status. But that's still more than he gets in the Dressrosa Arc. In that arc, all Kinemon really does is run around with the Straw Hats...and run around some more...and not do anything special. The only thing Kinemon really does to help anything comes several chapters in, when he disguises himself as Doflamingo to make a petty distraction which doesn't work all that well. And with the major threat of Doflamingo plus the introduction of Issho and the colosseum combatants, as well as Sabo's return, Kinemon is nothing anymore.
Ultimately, Kinemon suffers from what I call "character juggling"; when the author has too many characters to give them all a spotlight. As an underground comic writer, I know this problem very well. Ultimately, Kinemon's real purpose, to add to Doflamingo's villainly, is rendered unnecessary due to the plotline with the toys. It would have been much better to add Kinemon after the whole Doflamingo business, if at all. On a side note, Kinemon's devil fruit is the weakest and most useless fruit ever, and it made me create this samurai proverb:
THE FRUIT OF THE DEVIL IS THE SAMURAI'S RUIN.
Aye.
Aye.
'
I'm so useless!
'
Do you agree? Or do you think Kinemon has some purpose in this manga?