Title comes from Genesis 4:9 - "And the Lord said unto Cain, Where is Abel thy brother? And he said, I know not: Am I my brother's keeper?"
"Luci?"
Lucifer ignores Amenadiel completely and pours himself another glass of whiskey with shaky hands. He gulps it down quickly, more quickly than Amenadiel thinks he's ever seen Lucifer drink before. Lucifer drinks a lot, Amenadiel is under no illusions about that, but he tends to drink slowly. He claims it's something to do with savoring the taste, although Amenadiel thinks all of his drinks taste absolutely awful. The fact that he's knocking back his whiskey this quickly is yet another sign that something is very wrong.
"Lucifer?"
Lucifer continues to ignore Amenadiel, bracing himself against the bar and breathing slowly. He hasn't objected to Amenadiel's hand on his shoulder, but to be entirely honest, Amenadiel is worried about that too. Normally, Lucifer would have threatened to separate his hand from his body by this point. Clearly, it's time to bring out the big guns.
"Sama-"
"Don't call me that!" Lucifer snaps, his voice thunderous. "Don't you dare call me that."
"I won't," Amenadiel replies, trying to sound gentle and nonthreatening. Lucifer is reminding him of a cornered animal right now, and it won't do any good to scare him off. "Luci, are you alright?"
It's a stupid question. Amenadiel starts kicking himself for asking the second the words come out of his mouth. Lucifer, for his part, whirls around, eyes flashing with hellfire.
"I'm not broken."
"I didn't say you were."
"I'm not," Lucifer insists. Amenadiel hasn't always been good at reading his brother, but he's pretty sure Lucifer's trying to convince himself more than anyone else. "It's the stupid sword."
"Lucifer," Amenadiel says gently but firmly. "I believe you. I don't think you're broken."
Lucifer stares at him, then deflates slightly. "Well. Good."
"I do think you're hurting, though. And…" Amenadiel is proud, perhaps too proud, but he's also Lucifer's big brother, and it's high time he starts acting like it. "And some of that is probably my fault. For what it's worth, I'm sorry."
Lucifer's eyes go huge. He lets out a little choked noise, and then he crumples to the floor and starts to sob.
Amenadiel kneels in front of him, wary of getting too close. He doesn't know what to do. Lucifer has never acted like this before, not in all the millennia that Amenadiel has known him. He hasn't ever cried like this, not once.
Tentatively, Amenadiel spreads his arms in what he hops Lucifer will recognize as an offer for a hug. Lucifer doesn't even seem to notice that Amenadiel is moving. Slowly, aware that this might get him punched, Amenadiel reaches a hand out and touches Lucifer's arm, as gently as possible.
Lucifer collapses onto him, still sobbing, his hands fisting around the fabric of Amenadiel's shirt. Amenadiel wraps his arms around Lucifer's shuddering frame. He keeps gasping for air like he's forgotten how to breathe, and he won't stop crying and trembling. Amenadiel has never seen him like this before, and he'll admit, if only to himself, that he's worried, maybe even scared. Lucifer doesn't cry. When he's upset, he drinks, and he has sex, and he buries his feelings as deeply as he can. He doesn't cry. The fact that he is…
Amenadiel wonders how long he's been hurting like this, and what he can do to help.
"We don't have to use the sword," he says quietly, once Lucifer's sobs start to taper off into little gasps. "We'll tell Mom it won't work and we'll figure out something else."
Lucifer makes a noise that sounds like a mix between a sob and a hysterical laugh. "What, and you think she'll accept that? You think we can just tell Mum she's not cutting through the Pearly Gates, not seeing her children, just cause lighting up the sword hurts?"
Lucifer's voice breaks a little on the last word.
"We can explain it to her," Amenadiel tries to say, but Lucifer isn't listening. Amenadiel hates to admit that Lucifer's probably right. Mom has always had a soft spot for Lucifer, but she also desperately wants to go home. She's not going to take no for an answer.
"It's fine," Lucifer says, shaking his head. "I'll light the sword up when we need it. It'll work."
"Luci, it hurt you."
Lucifer bares his teeth. "I can handle it," he spits. "When it's time to cut through the Pearly Gates, I'll light the sword up."
"Lucifer-" Amenadiel tries, but Lucifer's mask has slammed back into place. He pushes himself upright and scrubs at his eyes with the heels of his hands. As Amenadiel watches, Lucifer pours himself another glass of whiskey, knocks it back, and tugs his shirtsleeves down to their proper position.
"Well," he says, sounding almost back to normal, "I'm going to go downstairs. Sounds like there's quite a party going on down there, and I wouldn't want to miss it."
"Lucifer-"
"You can come down with me, but you might end up having fun." Lucifer frowns. "Are you still allergic to fun, or has Maze cured that?"
"Lucifer-"
"See you later, brother!"
And with that, Lucifer disappears into the elevator. Amenadiel could follow him down into the club, but he doesn't particularly want to go down there. Anyway, this might be what Lucifer needs. Drinking away his feelings sounds more like Lucifer than crying and talking about it.
He'll be fine. Lucifer's always fine.
Amenadiel clears out of the penthouse - Lucifer's very likely to bring company with him when he returns, and Amenadiel doesn't want to be there for that - and leaves the building. For a moment, he considers going off to find his mother and talk to her about other potential options, but he can only imagine Lucifer's fury if he finds out Amenadiel went behind his back like that. Instead, he just goes back to his office, sits in the dark, and tries to convince himself that he really is glad they've almost figured out a way to go home.