The hardest thing about playing the angel is the way he treads the love-hate line with everyone else in his canon. It makes every first time thread I have with any castmate delicate, because I need A) to keep Balthazar in character and B) not kill the interaction by means of him being a total jackass. Now, my inclination in RP is to always err on the side of the character being too nice, because…that’s me and I’m a people pleaser. But you can only go so far that way with Balthazar before he turns into a big drunken woobie who’s mooning around after Cas, and I’d be doing a disservice to the character if I let myself play that (it’d be fun, though).
The fundamental element of Balthazar’s personality that I focus on is his ability to love. Not ‘love’ like flowers and hearts and romance, but love like ‘I think you’re doing literally the dumbest thing you could be doing right now, but I’m with you anyway’. I wish like hell there was more canon of him and Castiel interacting (not to mention Balthazar and ANY OTHER angel), because I’d love to hear the conversation when he and Cas decided to use the Winchesters as a diversion so they could retrieve the Heavenly arsenal. Or when they decided to unsink the Titanic. It’s easy to chalk it all up to Balthazar being a loose cannon (and oh god is he a loose cannon), but somehow I don’t think either of these gambits were completely his idea. In the Titanic episode, especially, he comes off as slightly edgy about the whole thing, both when he talks to the boys and later when he sneaks up behind Atropos. There may not be any rules any more, per se, but there’s still a chance of backlash, and he can see that.
His relationship with Castiel is really just a slightly more intense version of the way he relates to all his family members. They’re important by virtue of being his siblings; the most important things he can imagine. In an ideal world, there would be balance in the host and the knowledge that they’re all loved and needed and connected, but the more Heaven breaks down, the more disconnected Balthazar becomes from his siblings, and his Father by extension. Seeing them leave was heartbreaking (and he resents Gabriel and Anna, in particular, for deserting him, although he may never say it in so many words), but watching the ones that stay start killing one another is even worse. So by the time we see him all disco-ed up in The Third Man, he’s really hit the skids. Imagine the mix of courage and despair it must take to strike out at the last living and free archangel, and then multiply it by the guts it would take to burn a bridge back to Heaven by hurting an older brother he genuinely loves.
When I first started playing him, the romantic in me really wanted to chalk everything he does up to him just being in love with Castiel, and I do still play him as attached to Cas particularly, in a way that really isn’t healthy for either of them, but especially for Balthazar. But I’ve come to feel there’s more going on in Balthazar’s head than just a crush on another angel. Certainly there would have been opportunities before Castiel left Heaven, if Balthazar wanted him, to speak up and try to do a little cloud-seeding. I don’t think it’s that simple. I think Cas is his closest sibling, that he admires his courage and devotion to a higher ideal, and because of that he’s come to see him as a microcosm of what the Heavenly family could be/should be. I think this is also why he chose Cas over Raphael. Every slight from Cas hurts because Balthazar feels it as a rejection from the entire Host, and he can deal with that and move on; the Host is flawed, he knows that by now.
He’s furious when Castiel supports the Winchesters’ right to question Balthazar over his freedom from a blatant threat of painful fiery death, but when he gets out of that, he’s happy to focus his anger on Sam and Dean, not on Castiel. He makes excuses for Cas because he’s his brother.
The break happens in ‘Let it Bleed’. That conversation in the woods is
deceptively simple but by the end of it, Castiel has implicitly threatened to kill his brother, and Balthazar knows he’s killed Rachel, thus proving Castiel is no better than the rest of the Host. Maybe in some ways he’s even more flawed.
Destiny and free will are pointless illusions, and all that’s left for God’s angels is extinction by their own hands. He has yet to see this conclusion disproven. He has yet to be shown that he’s anything more than disposable to his siblings, in fact, but he keeps coming back for more, because while he was able to leave Heaven physically, he can’t actually let it go.