&Sin; love child
communicationSin is Ky's son, conceived from his wife, the unnamed woman from the forest. Yes, you heard me right - son. In Guilty Gear 2 Overture, Ky fell in love with a Gear, whom many speculate to be Dizzy (you may read more about in the Dizzy section). So much was his love for her that, well, let's just say Ky is now "grownup" in the sense of romanticism. Therefore, Sin is partially human, partially Gear (though the fractions may not be 50-50 per say). He not only looks like Ky with his hair, eyes, and blue/white clothing, but gameplay-wise, Sin holds the same "tribe" as Ky's. His Master Ghost is also the same with Ky's - a symbol of his mother. Sin also has a similar personality with Ky in the sense that he rivals Sol, and even hates leaving things undone.
But when we see Sin and Ky meet again, it isn't a happy reunion. Sin reflects an average teenager who holds some hostility towards his father. Sin's relationship with Ky had been rocky because of Ky's neglect. He spent much of his time dealing with his kingdom that he failed to share the love with his wife and child completely. Sin felt Ky was so concerned of his status that he was ashamed of his family. After all, he and his mother had to be in secret from the king's affairs. In turn, his mother was suffering now because Ky couldn't save her. He couldn't do anything for them.
Sin represents the mind of an average teenager. Because of his lack of attention from his father, he becomes emotional and easily hurt. It made him question his worth, and his mother's worth, to Ky. He felt as if he didn't matter to Ky, as he was ordered to go with Sol in order to prevent persecution. Like most teenagers, Sin doesn't hold back insulting and arguing with his father, and running off with his new 'father' Sol. valentine manipulated this emotion and empowered the dark feelings in him (Devil Sin).
Sol eventually regains Sin's senses, reminding him that it was Ky's stubborn justice will that has let him live. In an army of enemies, Ky joins Sin, and consoles him about his faults and his hope to patch things up. Sin is still slightly upset, but the news of their mother being alive gave him a slight sense of hope. He finally stops behaving like a brat and tells Ky one thing:
[NOTE: rough fan translation - I like this better than the English version]
Sin: When I was a kid, mother said that you were busy protecting many families. But with your downcast eyes, you'd never meet mine. Seeing the side of your face like that, I always thought it strange. Why were people you've never seen before so important? Were we neither family nor people? What was I? ..But still, mother said you are irreplaceable family. That's why...! That's why... I'll fight for mother. For mother, this time only... I'll protect your back!
At the ending, Ky finds all the characters (Sin, Izuna, Sol, Dr. Paradigm) in a field. Valentine's threat is over, but the truth being the Gear sublimation is still active. Dr. Paradigm needs more time to deal with the seal, so Ky offers him a place in the kingdom. Sin decides, rather than to chase after Sol, he would stay with Ky to see his mother again.