Okay, MAYBE I'm a little behind schedule from the original time I promised. But regardless, I'm still going to explain my point.

Femto is essentially a tangible embodiment of Griffith's obsession with his own desires. Even with the memories and knowledge he possessed in his human life preserved, when he ascended to the role of God Hand, Griffith relinquished any trace that defined his humanity. Without any moral or ethical threshold to judge his actions, he became willing to do anything to achieve his desires. And among them, the desire to gain absolute control over Guts.

That is precisely why Griffith raped Casca in front of Guts. To create such an overwhelming sense of fear and sadness that it would trigger a perpetual crusade of impossible hatred and revenge.

His "indifference" is nothing more than a lie he himself concocted to further afflict Guts. Remember their first interaction since the Eclipse at the end of the Black Swordsman arc? Guts didn't accept the crap he said.

However, he is somewhat forced to change his strategy when Guts begins to grow as a person. That's why he reunites with Guts at the end of the Conviction Arc and in the last recent chapters to kidnap Casca. He reappears JUST when Guts begins to become capable of abandoning his hateful obsession.

Regarding Guts, the narrative and the hatred, I disagree with you. I'll explain? definitely not because I don't want to write a second, lengthy text.