Lmao, Dair is not safe, ever. There's no good way to use dair that leaves you safe. The only time you're not punishable is if you edge cancel it, because the last hit of Dair when you land is extremely punishable(11 frames whoooooooo) Fair is much less punishable on shield, or on anything really.
And as for coming down with Dair, if your opponent is below you, whatever they have, Uair/Utilt/Usmash, will usually beat Dair. It's not particularly disjointed, and even if you dont get outright beaten, a clash is also a super negative for kirby since his multi hit Dair will only get 2% out of it while other characters will get a full hit. Dair is probably Kirby's second worst aerial, right in front of Nair.
And as for coming down with Dair, if your opponent is below you, whatever they have, Uair/Utilt/Usmash, will usually beat Dair. It's not particularly disjointed, and even if you dont get outright beaten, a clash is also a super negative for kirby since his multi hit Dair will only get 2% out of it while other characters will get a full hit. Dair is probably Kirby's second worst aerial, right in front of Nair.