Kirby appears in Donatello #1. He is first seen in his office space drawing a fly creature with his pencil as Donatello peaks through the door. The fly creature Kirby just drew startles Donatello which in turn startles Kirby. Kirby is surprised since he didn't remember drawing him and comes to the conclusion that he must be real. He assumes Donatello has come for the crystal and defends that he was only borrowing it for a while. Donatello assures Kirby that he is a friend and questions him about how he made those drawings come to life. Kirby tells him that it was the crystal on his pencil that supplies the "magic". He explains that he had found the crystal by accident a few months ago and discovered what it could do. He then shows Donatello a doorway he had drawn that didn't go away, unlike the rest of his drawings. Donatello steps through the doorway, and tells Kirby that he must see what's on the other side.
Grabbing his sketch book, Kirby jumps through the doorway and is caught by Don. They then spot a strange looking creature with horns which Kirby recognizes as something he has drawn. They both witness more of the strange creatures attacking the human types. Noticing the struggle against the amount of creatures, the creatures spot our heroes and close in on them. Kirby helps Don out by drawing him, what he calls, a "Gravitic Equalizer" that cancels out the gravity equation. He then draws Don a "Mobile Creep Trapper" that responds to brainwaves. He notices that the Trapper has filled up quickly, Kirby tries to think of another way to stop them. Realizing that the creatures are all in his sketchbook, he quickly draws all of the creatures bound with metal cuffs making it so they cannot move or fight.
The human fighters thank Kirby, calling him a "mighty sorcerer". Donatello tells him that they should probably go home, although Kirby shows interest in staying around in this world and exploring. But then both of them notice that the doorway from whence they came is shrinking. Kirby tells Don to go through first and helps push him through. Realizing that he won't be able to make it through, Kirby sends a note through the doorway instead; Don--"Life at best is bitter sweet" Take care of yourself! -Kirby
In the RPG Appendix Transdimensional Teenage Mutant Ninja Turtles values for Kirby are specified as part of a possible game scenarios in which he has developed a new life in his world, along with some new skills in martial arts, which he could learn from the local warriors.