I think it would be very easy for a Post Perse fading! Apollo to justify working for Kronos.
An Apollo who has seen the love of his life, his wife basically, die and the gods move on. Slowly, agonizingly slowly, but there's over a thousand years between Perse fading and the Great Prophecy, so they change nevertheless. They forget their children, used to someone else taking care of them, and when they remember its to send them out on a quest. Children leave camp younger and younger, and don't come back. Even Chiron, his old foster son, grows complacent, too comfortable sending babes to their deaths.
Apollo tries to keep his head down and be the best father to his children as he can. To some, he was their only parent; his children tended to pop up when a mortal reminded him of Perse in a particular way, often without sex (he was a widow, not chaste), and sometimes that resulted in them abandoning his child. Perse never would have abandoned a child though. She would have loved them. Michael. Kayla. Austin. Lee. Will. So many before. So many after.
But his children keep dying. Everyone's children keep dying, and no one cares, like Perse meant nothing to them and Apollo.
I never really understood how Ares was the one to catch Luke with the Master Bolt instead of, you know, the literal hunting gods.
And Apollo doesn't really want to help Kronos out, but like... he's going to need some sort of fire power and/or distraction so he can chop Zeus into little bits. Gramps can have the throne for all he cares, just leave Apollo alone with his kids and they'll be fine.
And Apollo would be such a good twist villain in one of these fics and you know what? Perse would think it was hot. He was doing evil to make a better life for his kids, that is DILF behavior and I won't stand for anything otherwise.
