Firing bullet after bullet into a being as powerful as Soldier Blue brings with it a supreme sense of satisfaction. Keith is only human, but he can fight monsters. He can dispense unto them what they deserve--
--and here, so close to the end, to humanity's first chance to destroy the Mu once and for all, he can admit that it's more than that. It's the knowledge that soon, Blue will retaliate, and dispense unto Keith what ihe/i deserves. Even if he's enough of a fool not to, the Megiddo will destroy them both. Then it will be over, and he won't have to think about what the Mu have done to Sam, what the Mu and Superior Domination alike have done to Keith himself, what humanity has done to itself.
One more shot, and then surely Blue's shield will fail. But now he is striking back, the blow spreading outwards, and this is it. This is the end. Keith aims to make that shot, and as he's aiming he hears a familiar voice and he resolutely ignores it, because Matsuka does not belong here except as a failsafe for if the destruction of the Mu fails and Keith needs to survive, and it has not failed.
Then it's too late and there are warm, weak arms around him and they are both gone, leaving Blue to die alone for the sake of his people and Keith to survive for the sake of his. In the moment that Matsuka teleports them away, Keith erases these thoughts from his mind. He does not need to remember that he wanted the destruction in that room to be more complete. Not until the next time he has the right kind of chance.
The next sound he hears is not the blaze of the Megiddo, but the simple thud of Matsuka collapsing around his feet. He's so busy suppressing other thoughts that he forgets not to cry out. "Matsuka!" But it's all right, because Matsuka is unconscious and cannot hear him.
Keith leaves him there to head back to the bridge. When he wakes up alone, Matsuka will have plenty of time to reflect on what he did and whether it was wrong. It's best if he learns that way, rather than having Keith tell him directly.
So it's not until that night that Keith sees Matsuka again.
He's holed up in his quarters on the Endymion, trying to plot the Mu's next move. It's a good thing Matsuka rescued him after all, he tells himself. The Mu escaped, which means that humanity still needs Keith Anyan. He tells himself that and is satisfied.
The door opens. Keith does not have to look up to know who it is. He can feel the familiar weak grasping at his mind, as automatic as the cringe that comes when he's called out for it. "Matsuka. I didn't ask for coffee."
"I don't have any," Matsuka says, and then there's that thud again. Matsuka has dropped to his knees.
This time, Keith does look up, because that's not part of the normal play of their interactions. Matsuka remains standing unless Keith throws him to the floor, no matter how much it takes. But this is a different Matsuka than usual. He is pale and trembling, cold sweat on his flushed face.
"You're ill," Keith says, standing up, "and you came to me. Why?"
"I was afraid," Matsuka says. "I was afraid they'd find out why I'm sick."
Keith stands over him now. He's a little surprised by the smile that forms on Matsuka's face, and a little irritated too, but he hides both feelings and only looks down at him impassively. "Aren't you afraid of me as well?"
Matsuka's teeth chatter. "I am," he says. "But you already know. Keith..."
There's no more point to words. Keith hefts that limp form from the floor, feeling him shiver violently as he does so, and slings him onto the bed. Unbidden, an old memory comes to him: Seki Ray Shiroe, trembling like this upon Keith's bed in Station E-1077. Keith forcibly banishes the memory. Matsuka is not Shiroe, and he never will be. He is weak and passive, and Keith keeps him only because he is useful. He knows better now than he did when he sheltered Shiroe.
"Thank you," Matsuka says. "Keith."
"Don't thank me," Keith says. "Learn to use your powers better, so you don't burden me like this again."
Somehow, Matsuka manages to cringe even while lying down and shaking with fevered exhaustion. Then he falls silent. Keith sits back down. It occurs to him that perhaps the crew will talk about what it means that Matsuka is spending the night in Keith's quarters, if they find out. He decides that it doesn't matter if they have such a misconception. For now, he sleeps in his chair.
When he wakes up, there is a hand on his, cool with sweat but warm beneath that. Keith moves fast, even half-asleep. He twists his hand around to reverse the position: now he is grasping Matsuka's wrist, pushing his hand upwards, just enough to hurt but not near enough to damage. On the bed, Matsuka startles and looks at him wide-eyed. He is no longer shivering.
"Why did you touch me?" Keith says.
Matsuka casts his eyes down. "I wasn't reading your thoughts," he murmurs.
That's not an answer, and they both know it. "Why?" Keith repeats.
"I wanted to know you were safe," Matsuka says. His voice is still a whisper.
Keith looks at him, and he does not let go of his hand. Finally, Matsuka grits his teeth with the pain, and then Keith does let go. It's enough. "Never touch me unless you have to," he says.
Matsuka sits up in the bed, and Keith realizes a little late that although he isn't shivering, he's still hazy with fever, exhaustion, or both. His eyes are a little glassy. "It felt like I had to," he says. "I'm sorry."
Keith has said all he needs to. He starts to look away, back to his desk where the information on the Mu rests. He has more important things to deal with than this one man, who is already thoroughly dealt with.
But Matsuka does not know he is already dealt with. "Keith," he says, his voice wavering. "I think you played with fire when you were little."
Nonsensical ramblings brought on by the stress of the day. Keith ignores the words and instead calls up a chart detailing the Mu flagship's last warp.
"I don't know if I can teleport like that again," Matsuka says. "Please don't do more things like what you did today."
That can't be ignored. Still, Keith doesn't look at Matsuka as he responds. "I'll do whatever is necessary. You'll teleport again if I need you to."
At the edge of his vision, he sees Matsuka relax back into the bed. He does not see the more subtle ways Matsuka moves. He misses the way Matsuka nuzzles the pillow and breathes deeply.
But when Keith sleeps, his arms folded on his desk, Matsuka's words come faintly back to him. I think you played with fire when you were little. No one else has ever said anything like that to him. Half-asleep, his control loosened, Keith cannot stop himself from wondering if it's true. But how would Matsuka know? One little monster surely can't see the urges Keith keeps hidden from himself.