In an interview with the design team, the first draft for Kirk's Thorn Armor was going to be based off Hydra from the manga Saint Seiya: Knights of the Zodiac. Art designer Daisuke Satake and director Hidetaka Miyazaki didn't see eye to eye with the initial concept, as Satake's concept was "a huge guy covered in spikes", so they reworked it.

The final design began to take shape when Satake and Miyazaki began to talk about the Trial of 77 Rings from the manga JoJo's Bizarre Adventure, in which two characters had to earn their knighthood by defeating other combatants and wearing the rings they had on them onto their body, collecting a total of 77 of them. Miyazaki and Satake both liked the concept and decided to see what it would look like if the rings also had thorns on them.