Well, I know pikachu's moveset fairly well, but I don't know nearly as much about kirby. So, I'll just give some of the things I generally try to do with pikachu, and you guys can discuss that.
So,
1) Pikachu's jolt
Yeah, one of pikachu's best tools. It can be used for camping, or to help approach (by full-hopping a jolt as you move towards the kirby) It can also be used while retreating to help the pikachu get a breather. When recovering high, I often send a few jolts to the stage to help out my landing.
2) Pikachu's grab game
I don't think Pikachu can CG kirby, even with the buffered grab, but pikachu does have some followups out of his grab. At low %'s, pikachu can F-throw to U-smash, and D-throw to N-air. I think Pikachu has the frame-advantage on these at low %'s, making them unavoidable. I'm unsure at what % they can be avoided at. As to other things pikachu can do with his throws, B-throw kills on walk-offs, and is great to toss an opponent off a ledge, U-throw sends an opponent high for juggling (or a thunder kill if they're careless), and D-throw is also a juggling setup at higher %'s.
3) Pikachu's Quick Attack
I don't know how good Kirby is at edgeguarding, but even MK's have trouble edgeguarding pikachu. Pikachu's quick attack has 2 jumps, and so can be used to go around almost any edgeguard. Add this to skull bash and pikachu's absurd ledge sweetspot, and you have a very difficult recovery to edgeguard.
And of course, there's the dreaded QAC. To the uninformed, this is pikachu quick attacking into the ground, which lets him immediately jump (this counts as his 2nd jump), and then do an arial/special move. He can also just immediately start an arial without jumping, but only D-air comes out, and only with its landing hitbox. Pikachu's QAC can lead to some awesome mindgames if used correctly. However, if the opponent keeps his cool, it is quite counterable, sometimes even with a kill move. (Once a Marth F-smashed me right out of a QAC...) However, that said, good pikachu's use it mostly when it is least expected to keep you off guard.
Also (as if that weren't enough uses), QAC can lock if you miss a tech. See
http://www.smashboards.com/showthread.php?t=238293 for an idea of what this is capable of. However, it is extremely difficult to do correctly, and only the best pikachu's will be able to perform it reliably.
4) Pikachu's air game
One by one here...
N-air: Pikachu's killing arial. This can get low % kills if used offstage, or can be used to end a u-air juggling combo. It is very quick to start up, coming out on frame 3, and does 12% if you're caught in it at startup. However, it has a fair bit of ending lag (and landing lag) if missed.
F-air: This can be used to juggle (although U-air is used more often in that regard), but is often used to start combos. When a fast falled F-air is used on a grounded opponent, pikachu has a frame advantage due to the hitstun outlasting the low landing lag. Follow-ups include grab, d-smash, u-tilt or perhaps a N-air. However, if you shield the f-air, and the pikachu lands in front of you, you are then able to shieldgrab.
B-air:
Probably the least used of pikachu's air moves, however, B-air has awful landing lag, and takes a while to do. However, startup and ending lag are pretty nice, and it tends to suck opponents in, before knocking them away with the final hit. It can be combo'd into from U-tilt or D-throw, but U-air/N-air is used much more often. Basically, this move is only thrown in once in a while to surprise you.
U-air:
My personal favorite, this is the primary juggling tool. It comes out on frame 3, does 4-6% damage and small knockback. This is often used to poke up at opponents standing on platforms above pikachu, and combo's into F-air, B-air, N-air, or even another U-air.
D-air:
This can be used out of a short-hop to punish shielded attacks, or as an unconventional approach. Landing lag isn't that great, but it has a landing hitbox that does 4% and pushes opponents back far enough that they can't punish. It doesn't have many other though. It takes the longest to start up, with frame 14 being the first hitbox.
5) Pikachu's Thunder
There are two main applications to this move, edgeguarding, and KO'ing. As far as the edguarding goes, the application is obvious, but pikachu has many different things to do with it, such as quintiple thunder (shown here:
http://www.youtube.com/watch?v=NeSlOCmR46A) and wavebounced thunder. As far as KO'ing goes, there's one main way to do it, and that is
Thunder chasing Basically, U-tilt/u-smash sends the opponent high, and thunder finishes the job. My favorite way to KO.
6) Pika's ground game
A few things you need to know...
D-smash looks broken, but if you DI up, you'll DI out of it. However, it is still used to give pikachu some breathing room.
F-smash has the longest range, but takes a while to start up. It's a pretty powerful kill move if you're close in, but not so much if you're on the edge of the hitbox.
U-smash is also a kill move, especially when combined with thunder. It's faster than F-smash, but is still one of the slower moves in pika's arsenal.
U-tilt is another kill move, but only when thunder is used. It also sends enemies into a juggle, making it used often.
F-tilt does decent damage (10% at maximum) and comes out pretty fast, making it another move pikachu uses when he needs some breathing room.
D-tilt isn't really used that much, but it still has okay speed and damage.
Pikachu's jab isn't used too much either, but it comes out on frame 2 (and every 5 frames thereafter), and is pikachu's other locking move. (But only when you are at 70% or more)
Well, that's pretty much pikachu's moveset and what it's used for, so what can Kirby do to counter it?