This is based on ch 232.1. I changed some of the order of events, but hopefully nothing out of the realm of reason.
Senku was glad he wasn't alone.
Would it have been safer, easier, to just drag petrified Kohaku along? Of course. He'd gotten better at things requiring strength, and he wasn't too bad at fishing and diving now, either.
(It felt like just last week he was saving Kohaku from being trapped under a tree. But no, it had been years and years. They were thirty now. They'd been friends for half their lives.)
He'd have survived just fine on his own while gathering the statues of his friends and making more revival fluid. But as she'd said, he'd wanted her there. A partner.
He asked her to grab some seaweed, then went about making rope and tying two palm trees together while Kohaku caught them something to eat. Less risk of rotation and suddenly being dumped into the ocean when they didn't want to be if they had at least two trunks to work with. Those tied off, he considered his next step.
For shelter…palm leaves would work. He pulled the leaves at the top of the trees over and up to make a shelter from the sun, then gathered more to weave a mat for sitting or sleeping on, then still more to dry out to burn. Next up was desalination, and maybe a place for fire.
Kohaku popped to the surface. "Senku!" she sang. "I've got dinner!" And proceeded to hoist the biggest fish Senku had ever seen in his life onto the raft.
"What the hell?" he said, laughing incredulously. "Where'd you find this monster?"
She pushed herself up to sit on the edge of the logs, leaning back on her hands. "Oh, just swimming around."
"Well, I think we're set for food, lioness," he teased, dragging the fish to be a bit more securely placed. "Probably for the next month or so."
She laughed. "More like a day! I'm already starving!"
Not surprising—she probably had a super high metabolism in general, and swimming so much would only burn up more calories. "Want to help me make a fire pit, then?"
She flexed one arm. "Ready! What do you need?"
He told her and off she went. Meanwhile, he put together his first attempt at a simple solar desalination plant.
As the sun started to set, they had the basics—food, water, and shelter. They shared a meal of salt-seasoned roasted fish, then sat and looked at the stars for a while.
"One more time," Kohaku said after a while. "I think I'm starting to get it. Stars are fire. I get that. Big balls of fire, floating in space, way far away. So far away that it would take thousands and thousands of years to get to one. And light…takes time to travel?"
"Yup."
"Hm."
He knew she was skeptical. "I could show you some cool experiments that show it when we get back to civilization. I bet Xeno has the equipment set up."
"Sure, I'd like that. So because light apparently takes time to travel—"
"It does!"
"—the stars we're seeing could be all burnt out right now. We just can't see it yet."
"Yup."
She tilted her head and hummed. "It kind of hurts my head to think about, the universe being that big, the stars being that far away."
"Humans aren't really built for that big of big numbers. You remember the hundred and fifty limit Gen talked about? We're wired for numbers for communities like that."
"Except you," she said, nudging his shoulder with her own. "Dr Stone, genius scientist of the New World or whatever they're calling you."
He huffed. "No, I'm the same as everyone else."
"Ha!"
"I mean it!" He suddenly found it hard to find the right words. This wasn't something he talked about, ever. But…well, he and Kohaku were as alone as it got right now, and there was no one else he'd rather talk about this with. "I…I learned this stuff, you know? I wasn't born with a better understanding of everything. I'm not a genius. I had to work for…all of it. I had to practice mental math. I had to practice remembering things and reading fast and all that other stuff." He kicked one of his feet back and forth in the water of the ocean with a sigh. "Maybe I'm good at counting, maybe I have a decent memory, but I worked for and practiced everything else, and it feels kind of lame when they call me a 'genius,' or treat me like I'm not even human or something. Like I didn't have to try and fail and try again until I got it right."
"I know," Kohaku said softly. "I've seen it. You're the most hardworking person I know, though, and I think that's still pretty special."
He glanced at her with a raised eyebrow. "Coming from someone who ran kilometers carrying giant jugs of water every day for years?"
She shoved him lightly. "Shut up! That was ages ago!"
"Coming from someone who sat down and wouldn't move until they learned all the kana so I would 'stop bugging you' about it?"
"Senku!"
He laughed. "Coming from the strongest person I know? That's something."
She grinned at him, leaning towards him. "I'm the strongest person you know? Really? Did I hear that right? Not Tsukasa or Taiju?"
He felt his ears start to burn at her scrutiny. "I said it once, I won't say it again."
She giggled, scooting close enough that he could feel the heat of her skin. They sat in pleasant silence for a moment before she said, "I get it. The genius thing. People have said all my life that my strength is 'sorcery' or 'unnatural' or something. Even now."
He frowned. "What, seriously? Still? The rescue crews you work with say that?" He hadn't known that—he had thought things were going well.
"Yup," she said with a sigh. "Like you said, though, I worked for it. Maybe I have a body built for strength or speed, but if I didn't try to improve, it wouldn't mean anything. I'd be as weak as anyone else. It's like…potential. I made use of my potential, but it was still work."
He considered what she said, staring at the water. He hadn't known she felt that way. Neither of them was the type to complain all the time, after all. But his earlier statement didn't quite sit right anymore, didn't quite cover all he wanted to say. "Then how about this: you are the most hardworking, loyal, steadfast person I know." He glanced at her, lit by the light of the moon and stars. "I'm honored to be part of your life."
Her eyes shone with light reflected off the water as she glanced back at him, a contented smile dancing across her face. "And I'm honored to be part of yours." She then did something he'd never seen her do —she bit her lip and turned away, reaching up with one hand to play with her hair. Had she ever been timid before? "No matter what happens," she said in a low, earnest voice, "whether it's crashing in a plane or landing on the moon, good times or bad, saving the world or just sitting here, I want to be by your side. For…for the rest of our lives, if I could do that, I'd be the happiest woman alive."
Senku realized, as his heart pounded a little faster, he had no idea how dating and marriage proposals normally worked in Ishigami Village. Chrome had just blurted out "let's get married" to Ruri (and after all that planning and rehearsing he made Senku sit through) and they hadn't even been dating, but that was Ruri and Chrome—they'd kind of decided to get married when they were kids and hadn't formalized it until recently. He didn't imagine Kohaku to be the type to ask unpetrified people about marriage or weddings just for fun, either, so she probably didn't realize how similar her words sounded to marriage vows in some cultures.
And he'd been wondering, recently, if this was where their relationship was going. Not with disgust or even trepidation, as he might have when he was younger. Even now, the thought of loving and marrying some unknowable future "someone" did not appeal to him on any level.
The thought of loving and marrying Kohaku did appeal to him. A lot. "A life where I can always stand beside you is maybe the most exciting thing I can think of," he said, meaning every word of it. Even the boring stuff—the domestic things and everyday nonsense—would be better if he knew Kohaku would always be with him.
Their world was quiet, limited to their breathing and the gentle splash of water. He could feel her breath on his skin as she looked up at him with wide eyes and slightly parted lips. "Senku…" she breathed out, and a shiver ran down his spine.
Slowly, deliberately, he lowered his head, watching for any hint or sign that she wanted him to stop.
Her eyes fluttered closed and she tilted her face up to meet his.
He'd never kissed anyone before. (He'd never wanted to.) He wondered if she had. One of them should probably have an idea what they were doing, right? Maybe they'd just have to figure this out together.
And then his lips were brushing hers, warm and soft, and he wasn't thinking about much of anything besides how nice this felt. She wrapped her arms around his neck and increased the pressure of the kiss, tilting her head a bit.
Tentatively, he moved his arm around her waist, setting his hand against her back. She moaned—a soft, humming moan then sent fire zipping through his blood—and he trembled at how overwhelming this was. He never wanted to stop. Could a person live on nothing but kisses?
It's just hormones, said his stupid brain. A natural biological response.
He ignored it and focused instead on the feeling of her fingers running through his hair.
But both of them were really tired after a whole day of hard work in an unfamiliar, unsafe environment, so their kisses naturally lowered in intensity until only their foreheads were pressed together, both of them breathing a little heavier.
Originally, Senku had planned for them to sleep in shifts. Their little "hut" didn't have much room, after all, and it was probably smart to have at least one person awake in such an uncertain situation.
But Kohaku was tugging him over to the palm leaf bed and pulling him to lay down beside her, and he couldn't find it in him to protest. They were lying facing each other, Kohaku's eyes still shining in the dark. "Good night," she whispered, her hands curled up by her face.
He reached up to cover her hands with his, pulling them to rest exactly between them. Tomorrow would be difficult—it always was—but as long as they faced the day together, Senku knew they'd be okay.