Griffith as Pure Evil
"Only the Greatest of all can make Himself small enough to enter Hell. For the higher a thing is, the lower it can descend — man can sympathize with a horse but a horse cannot sympathize with a rat."
-C.S. Lewis, The Great Divorce.
If someone asked me why Griffith was my favorite villain of all time, it'd be for myriad reasons. I think he's excellently written in so many ways; a textbook example of not realizing you're in a bad relationship until it's too late, a classic malignant narcissist, an extreme amongst extremes. He's one of the most believably evil characters I've seen in a long time.
A relatively common argument I've seen amongst Berserk fans is that Griffith and Femto are two separate individuals. I'll admit: I subscribed to this myself for a brief period, although in a more Kirkbridian way than most. My idea was that Femto and King Griffith of Falconia were two parts of a larger GRIFFITH oversoul, kind of like Akatosh, Alduin, and Auri-El making up AKA-TUSK. I don't subscribe to this anymore, but I think the idea is pretty cool.
Anyways: Griffith. Not Femto. Not after the Eclipse. Griffith. Golden Age-era Griffith. He's already a horrible person. I said it, I'll continue to say it. By the first time we see him, Griffith is an awful human being. He's already a textbook example of a malignant narcissist and an abuser, constantly manipulating and demanding the respect of people around him, lacking empathy for nearly anybody, treating the people he's supposed to care about more like dogs than people, only truly befriending people he thinks are "worthy" of his respect (i.e. only Guts), and so on. By the time we see him in the Eclipse, Griffith has already shed away any of his few redeeming qualities. I've seen an argument before that Griffith is "morally gray". I could not disagree more. Griffith is pure evil. He's a power-hungry control freak of a narcissist, blinded by his own ambition and self-righteousness to even consider the people around him. This didn't go unnoticed, either. Judeau noticed it after the death of the Queen, openly wondering if Griffith and Guts were involved.
And this isn't the only thing Judeau has noticed. Judeau was the only person to notice Griffith trying to strangle Guts after he was freed, and earlier on he actively sums up Griffith in the best way I think exists in canon as of now: being unsure whether to classify him as a "good guy" or a "villain", or more accurately, an adult or a child. We know very little about Griffith's past. All we know is that he was born in poverty but always had an ambition to become a king. I think that it's rather likely Griffith was raised as an orphan; he had nobody to look up to except for the king in his castle, who he wanted to be just like one day.
Griffith is tragic. He wants companionship, but it can never be given to him. He makes mistakes, but never learns from them and instead only blames other people. At the same time, though, he's evil. He's completely focused on power of any kind to the point of raping two women and sacrificing the entirety of the Band solely for his own personal benefit. He grooms and then pressures Charlotte into having sex with him (read: rapes her) because he was emotionally lashing out and because he wanted a chance to become King, not because he had any sort of emotional attachment to her. Likewise, he raped Casca to hold some sort of power over her and Guts and to spite Guts, but I think there's one more thing there: to convince himseld, and reinforce to himself, that he holds power. Ultimate power, especially over Casca and Guts: the only people in the Band that may theoretically hold more respect than him. He's petty, he's always been petty, and he will continue to be petty.
The scene where Griffith attempts to rape Casca in the carriage, when he's still crippled, has a lot of people on a lot of sides. Personally, I think this is Griffith's last little semblance of humanity clashing with the rise of Femto in his mind. He wants to rape Casca here. He wants that power back. He wants control. It is so tantalizingly close, if only he could move his body... but then Casca shows compassion to him. She shows Griffith that he is still loved despite his injuries and his failures. After a moment, Griffith acquiesces. He stops his impulses from taking over his mind, for the first time in... who knows how long, honestly. It nearly works, too. Guts almost stays, but Casca pushes him away. She tells Guts to take his own path. Guts agrees, and this enrages Griffith. Guts betrayed him. Casca betrayed him. Who else could he fall on? He couldn't even fall on himself. His ego is dead. His dream is dead.
Griffith sees what life would be like if he doesn't take the Godhand's offer in the Eclipse. He would remain human; he'd be taken care of by Guts and Casca, who are raising a little Guts Jr. and living a happy life. He'd still be disabled and spiteful, but he'd be human. He'd be... normal. Griffith doesn't want that. Griffith can't have that. He wants to be King. He needs to be King. He needs to be someone. He can't be no-one.
If he's normal, then he's nothing at all.
"Satan; so call him now, his former name
Is heard no more in Heaven."
John Milton, Paradise Lost.