With my recent discovery of this concept sketch of Ky from the 10th Memorial Book, as well as discussion about it, I actually wanted to talk about some of the misconceptions had with Ky's eye and its relation to his Gear Cells.
Long story short, we know very little about it.
The first time we hear about any issues regarding his eye is in Sol's Overture Material Collection short story. The eye patch is mentioned once, but never directly explained. It's also stated to be on the opposite eye in this image and that his Dragon Install is on. There's a claim that Ky's short story mentions a training accident that explains the eye patch, but it doesn't. The eye patch is only mentioned in Sol's, with no explanation. (Thank you @solradguy for these translations!) The other main theory is what I kindly dub the "Eye Swap Theory." Basically, people believe Ky has one of Sin's eyes. This one is a bit weird in all honestly. The main reason people believe it is because of a line added in the English GG World text for Dragon Install
The Japanese text says pretty much the same as the first paragraph of the English text. A very very rough translation through DeepL:
"A technique in which Sol removes the Gear Cell Suppressor and activates the Gear's original power. It can produce extremely powerful power, but Sol hates using it in the dark because it makes his emotional suppression ineffective. Also, each time Sol uses this technique, the growth of the ‘seed’ that lies dormant inside him accelerates, and changes appear in his appearance and abilities."
Regardless, it does not have that second line about Sin or Ky that the English text has. I have no good explanation to why it was added only in the English localization. It is not present in the Korean text either. I haven't check other languages. In my personal opinion, it’s hard to say that this factually the cause due to it only appearing in some translations. The only actual reasoning we are given for Ky's Gear Cells is a vague answer from Daisuke in a Famitsu Q&A where he is specifically asked about Ky's Dragon Install, and specifically asked if Sin was involved. Daisuke responded: " この場でお話することはできないのですが……。ディズィーとカイの関係が影響しているのは間違いありません。これ以上はご勘弁を（笑）。"
Basically, he says he can't talk about it here, but "The relationship between Dizzy and Ky is definitely an influence." In conclusion...we really don't know much about Ky's Gear Cells or his Dragon install haha... We know he wore an eye patch prior to Overture. We know he exhibits a red eye, regenerative abilities, and inhuman strength by Xrd. We know by strive he has a partial Dragon Install and claims to have the "Blood of Juno." No exact reasoning for any of these is fully given and information is confusing. Honestly, it seems like many plans were changed, or rewritten, but its hard to say. The 10th Memorial book does not mention it to my knowledge. It's fun to speculate though!
