yeah kirby is so~ hard to beat if you actually fight him, all of his stuff is safe on shield and we have no answer to bair bar needles. if you try and force your way in you'll be very disappointed. AT least that's how I feel.
In that situation where you have no real options remember this.
you move faster than him in the air.
You can always recover to the edge.
And worst possible case use upB in a way so that you can only be punished be a weaker attack.
Jump and recover high to a plat (again using upB crazy early if need be)
or fastfall underneath and use upB invul to avoid any possible hit even while in kirby's range.
if kirby is off stage trying to hit you he, for the most part, can't punish your lag from vanish because his aerial movement speed is so bad. (this is the case with most of the cast, but especially Kirby).
If you are in a situation where you are way off stage you can't jump or already have and your recovery options are very very linear then just take the bair and DI it well Bair helps you recover if you DI it correctly especially since it will prob be decayed in the first place.