I honestly do not know what to do in this match-up. Kennen has consistent, long range harass, really annoying stuns, mobility, and a game changing ult. Is there anyway to beat him in lane or otherwise without abusing one of his counters?
Kennen has been OP for over a year now so don't feel alone. A tip I guess is to play another bursty champion into him. Think of it like it's mid lane instead of picking a tank. All the juggernauts and people alike them can be easily kited by Kennen with his stun and E, so you're better off playing some AP champion (so he doesn't rush Zhonya's) like Fizz or LeBlanc and hoping for the best. If you have a competent jungler, that should help tremendously as he is a semi-assassin and is therefore squishy.
Kennen's damage falls off quite a bit unless you feed him. Even a little bit of MR will mitigate him heavily, leaving him to be only a squishy ult bot. Use masteries/runes and items that can help you sustain early and just play it safe for a little bit. Or play something with hard engage/heavy burst and outright kill him.
Same thing you would do against a Gnar. Get jungle to gank twice, you just won lane for good. Or get your teams ADC up there, more effective than gank, unless jungler runs full AD. Honestly just gank him. He's very similar to Gnar in playstyle. If he gets to easily cs lane, or gets an easy kill or two, his late game=GOD. If you manage to get that extra gold boost, he will be forced to tower farm, and thus, can't do crap.
Kennen is not that mobile of a champion. His move speed bonus is limited and, like all abilities, has a cooldown. Take advantage of the seconds in between. Try avoiding using your abilities against him in his lightning ball form because it grants him additional defenses.
Most of his damage requires him to place himself dangerously near his targets. He is incredibly squishy and his stun requires him to stack his passive onto his targets. Try to stay near your turret so he cannot commit to a full attack. Poke him down with whatever ranged abilities you have and, when you've whittled him down to a fraction ofhis health, bait him into a fight and finish him off.
His ultimate, while powerful, has an insanely high cooldown and it does not pay for him to build CDR because of his energy resource. Avoid clustering with your allies when his ult is ready for use. If he becomes a serious threat to your team then assemble your allies to swarm and end him in between his ult castings.
Merc Treads, Mercurial Scimitar, Banshee's Veil, and Maw of Malmortius are all useful defensive items to use against Kennen.
