Sol has always considered Ky to be “just a kid/spoiled brat” in most instances of their encounters.
But at the same time there’s a hidden dynamic to Sol towards Ky that suggests he feels sympathy towards Ky’s life.
It might seem obvious in hindsight, but Sol feels ‘guilty’ about the world being reduced to the state it’s become.
He’s felt regretfully responsible for unleashing the Gears in the world in the first place, even expressing as much when looking back on its history with Magic (when talking with Dr. Paradigm).
Ky was born in a world invaded by deadly Gears, his world was destroyed by them. And he isn’t the only victim of this tragedy (Johnny’s father was killed by a Gear as well).
And yet Ky chose not to give in to despair and place blame on the Gears themselves, but on those responsible for their creation.
This places an even greater guilt on Sol than you might realize.
Bad enough that Sol was hiding the fact he was a Gear from Ky.
Sol became the very thing he was responsible for creating… perhaps to atone the remainder of his immortal life as a living weapon.
Worse, he had to dirty his hands in the deaths of Gears who didn’t deserve to die, whose only crime was being born as a weapon like he himself had become.
Ky chose, despite his position and situation to instead offer a hand of mercy and protection to a woman born as a Gear. To love her as a person.
It might even be said that Sol is to blame for their union. He spared Dizzy and took away the reason she had to die.
Sol can’t take back Dizzy’s origins, nor can he take back Ky’s bloody past… even if he destroys “That Man” on a quest of vengeance.
When Dizzy gave birth to Sin… Ky’s role as ‘a Human outsider’ ended. Everything changed, and Ky was driven in to an ethical corner in his conscience. He felt the Guilt that should have only been Sol’s responsibility and onus (something Sol never told him).
In a true sense by a creating a Gear with his own blood, Ky had sinned against Mankind.
So a “Sin” was born. And Ky could do nothing to protect him in his situation. Ky was trapped and felt the only way to absolve himself was before God. He had lost his reason to uphold his sense of justice, his reason to continue fighting… because if he continued to fight, the one thing he treasured most (family) would be destroyed.
He’d already lost his family to the Crusades. Even if his family were Gears, he couldn’t afford to lose them again.
Dizzy knew he was suffering, so she called the one man she knew who could save them all… Sol.
So, on New Years’ Eve, Sol stepped in the Church Ky was confessing to God in… and defied God.
Sol was always antagonizing Ky… it had always been that way… but this time, Sol had to bring back what Ky had lost… his ability to fight.
I’m sure Ky’s sword arm had gone dull over the peaceful years of living with Dizzy, he’d forgotten what it meant to protect a person with one’s own life.
Sol was merciless in that regard, and yet Ky kept getting back up, loss after loss. Because Ky believed in HOPE.
Sin stepped in between their fight, risking his life against Sol’s sword… despite his hatred for his despondent and weak father. A small voice, yet a determined one, just like the father’s he hated.
What Sol saw before him was yet another innocent Gear being born in a bloodstained world. His own doing, not Ky’s.
Sol knew that Ky was the only man he could trust to represent humanity. This was exemplified with Ky’s “death” (in an alternate timeline).
Kliff Undersn (a man who had fought Justice and survived for most of the Crusades) had accepted both Ky AND Sol in to his own family, with no doubt or hesitation in his heart.
Sol probably even considered Ky like a son, perhaps.
Ky told Sol the truth of the matter, and asked Sol to take care of Sin during this turbulent point in Ky’s life, being put in the role of a King.
If Sol was just a scientist who only cared for results and would not accept failure… if he was his past self… he might have said ‘No’ and declined to Ky’s desperate request.
But war changes people. Heated rivals can become blood brothers… even family.
And perhaps there was another way in which he could atone for his past as “Creator of the Gears”… by raising Sin up like his own.
Sol’s rivalry with Ky remains, but now they both fight for what they believe in. Even if it’s just a little, some understanding now exists between them.