You main Ness?
I would have never guessed. Okay, so it'd help if you told us what he does, but I might already have an idea of what he's doing.
In the first part of the fight, Kirby will most likely grab > f-throw > uair > if not grab > f-throw > grab > f-throw > uair. Is that even possible to pull off? No idea. That's what mosts Kirby's I've fought like to do when I'm at 0%. For his Final Cutter, if you're at a distance, just absorb the beam that fires out. I do believe Kirby is light, right? Juggle him with PKT. It's best to use the tail of PKT, too. If he decides to use his Stone, the tail will sustain him in the air. That's the part where you must figure out how to escape from getting hit. I usually hit myself away if it's possible.
When you're off the stage, Kirby's got many options of how to defeat you. He can use his Drill Kick, he can use his Stone above your PKT2 to avoid getting hurt in the process or he can suck you up and spit you out. Of course they usually like to use the Drill Kick or Hammer on you. Whatever the case, there is a way to work around these. Save your second jump. At least you can use uair, fair, nair, dair (if he's below you for some reason) or you can just simply air dodge. As for his Stone, that's difficult, but not very many Kirby mains use this one.
If he sucks you up, it's not impossible to escape it. Usually I end up footstooling Kirby when I escape and if necessary, I use PKT2. Does this Kirby just f-smash over and over again? If so, try to dair him. I'm not exactly sure that'll work, but it's worth a shot, I think. I've been lacking in the Kirby match up department lately, but there might be others that have greater ideas.