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As a child Senku found it hard to sleep, insomnia if you will.
Instead of falling asleep as soon as his head hit the pillow like most children his age, his mind was awake, rampant, restless. Thoughts running around, experiment ideas popping up, Senku's mind was constantly awake, it was hard to force him asleep when his brain was so eager to do something.
Eventually, after the nights without sleep piled up, the exhaustion was begining to show on his face. Big, dull purple eyebags stretched under his eyes, contrasting his son's youthful face. As soon as the marks came formed, Byakuya was quick to take notice, and immediately began to search for solutions to help.
He began to introduce these ideas to Senku, hoping to get a successful result somewhere. Reading before bedtime, listening to calming music, drinking a glass of warm milk, and countless others were all potential solutions he presented to the boy. But nothing was working, and the pair began to get quite irritated, for different reasons.
For Senku, the lack of sleep had begun to get to him, messing with his thinking process as well as his mood. Formulae that were a piece of cake for Senku suddenly disappeared in his mind, questions that Senku could previously answer in his sleep began to eat at him, his memory becoming foggier and his movements sluggish. He wasn't considered an even-tempered kid, but now, with the lack of sleep, he began to become more snappy and grumpy.
For Byakuya, he became increasingly worried with Senku's sleep schedule. It was no secret that Senku's biological father had trouble sleeping aswell, but to see that being passed onto the stubborn, hardheaded boy he'd came to love as his own, it hit differently. Unlike Senku, Byakuya was sentimental and mushy all the way to his core, and the sinking feeling in his chest became too much to bare staring at his sleep deprived son, who seemed way too stressed for a boy in elementary.
The constant mistakes only haunted the boy more, echoing in the distance, and people in his school life began to take notice too.
Byakuya remembered one evening, he got an email from a sender didn't recognise. After a few moments of reading, he found that the sender was Senku's elementary teacher, who was worried for his well-being. She was a young woman, fairly new to teaching and if Byakuya could recall it was her first time teaching elementary students. She suggested some solutions for Senku, but it was nothing that two hadn't tried. The man sighed, rubbing his temple.
'What to do, what to do..'
The idea struck him like a hammer to a nail, it sounded simple enough, and at this point Byakuya was ready to try anything.
A light knock interrupted his thoughts, and a fleeting glance at the clock Senku made told him it was 11:53 PM. Definitely way past the boy's bedtime. (But really, when had he ever followed it anyway?)
“Senku? Is that you?” He called from the bed.
The boy behind the door made no acknowledgement to Byakuya's question, simply opening the door and staring into the man's soul with the same awkward, constipated expression that Byakuya had chalked up to (after many times of seeing it) 'I can't sleep and I'm too stubborn to admit that, but at the same time I want you to stay by my side and try and help me sleep'.
“Trouble sleeping again?”
No response.
“C'mere.”
Senku stepped into the room, and walked over to the bed, not before closing the door though. (Because he was civilised, unlike certain people, *cough* *cough* Byakuya *cough* *cough*.) He crawled closer to Byakuya, and made himself comfortable under the covers. The man smiled down at him, pretending to fix his son's hair, and not so discretely pinching his cheeks while he was doing it.
“Hey!”
Senku whisper-shouted, his tiny baby face scrunched up and offended in a way that Byakuya could describe nothing less from absolutely adorable.
“Alright, alright, I won't annoy you..” He trailed off, pretending to have finished his sentence. “For now.” He gave Senku a shit-eating grin, watching the boy's face contort into one of exasperation. Exasperation that only made the love he had for his son grow.
“I regret coming here.” He groaned, turning away, almost sulking (but he wouldn't admit it even if he was dying), and Byakuya only chuckled louder.
”Hey! Don't be like that” Byakuya pleaded, reaching out to him and slightly tugging on the boy's shoulder, until his son gave in, and turned back around to face him.
Senku let out a yawn, and Byakuya remembered the current problem they were facing.
“Hey, Senku. I have a silly idea, but you have to hear me out 'kay?” Byakuya proposed, watching the gears turn in his son's head.
“If it's any better than drinking milk, then I'll hear it.” The older man laughed again, remembering his son's distaste for milk.
“Don't worry, I won't be making you drink anymore milk. Atleast, for now.” He eyed his son's skinny arms, another problem he had to fix, though this one wasn't giving Senku as much trouble, so he'll let it be for now.
Senku snuggled closer, trying to escape from the drafty October air that circulated room. “So what's your idea?” He asked, looking at his dad with rapt attention. The boy was just as eager to find a 'cure' for his insomnia as Byakuya was, if not more. The lack of sleep had been tampering with his experiments and causing him to be sloppy, something which Senku did not appreciate.
“Have you heard of counting sheep?” Byakuya inquires and watches as his son's face changes from eager to irritated.
“Sheep? Really? I'm not five, dad.” Senku deadpanned. (As if being six was somehow so much greater than being five, but Byakuya decided not to bring that up for now. It was clear that the sleepless nights had begun to mess with him more than he thought.)
“Hey— I thought I told you to hear me out— And it doesn't have to be sheep.” He compromised, watching his son perk up slightly again, even though he was trying to hide it. Byakuya knew the boy far too well, under Senku's stony exterior, there lay a heart just as emotional and mushy as his own. Even if the boy himself would never admit to it.
Senku turned on his back, staring at the glow in the dark stars that Byakuya put up a few nights ago. (He was going to order it sooner, but when Senku caught wind of it, he demanded scientifically accurate constellations, and who was Byakuya to deny his son?)
“'Kay. I'll try it, but if it doesn't work then don't be surprised.” Senku said, like it was meant to be an insult, but Byakuya knew better. The man chuckled and watched as his son started counting aloud.
“One.. Two.. Three..”
A few more numbers in and Byakuya realised that Senku wasn't counting in a random order, he was counting the seconds. He looked at his son with a fond smile, it was so in character for him.
Four hundred and twenty-seven seconds in Byakuya, to his suprise and excitement, began to see Senku's eyes drooping, and in-between six hundred and sixty-eight seconds and six hundred and sixty-nine, the boy finally fell asleep.
Byakuya carded his fingers through Senku's unruly hair, for the life of him he never knew why it stood up like that, and his small, fond smile turned into a wide grin. He felt relief, that his son wouldn't be tormented with insomnia any time soon. God knows how much it hurt seeing his son in pain. (Even if he was never very religious.)
Careful not to wake his son, he slowly retracted his hand and began to try and go to sleep for himself.
The blanket lay over him up to his chest, warm and soothing. His eyes drooped but he didn't fail to notice how Senku, in his sleep, began to curl up next to him, seeking his warmth. Byakuya put a arm over his son, and smiled at his sleeping face, knowing that the big marks that stood out under his eyes would soon fade.
He goes to sleep with a fond smile on his face, arm draped over the boy he called his son.
That was the last time Senku couldn't sleep.
Ever since that day, counting his way to sleep gave him comfort, relief even.
The night before Byakuya went out into space, fifteen year old Senku knocked on his door once more. His knock was more firm, more heavier, but Senku all the same.
Byakuya called out to him, and much like his six year old self, Senku gave Byakuya The Look™ and Byakuya took that answer in stride.
The man patted the space next to him, devoid of any mocking or teasing, after all, he was getting a bit sentimental too. The two snuggled up unto the covers, Byakuya facing Senku, and Senku facing the ceiling.
And much like old times, Senku began to count aloud. His voice was deeper now, lacking the childlike glimmer he had when he was six.
Four hundred and twenty-seven seven. His eyes drooped.
Between Six hundred and sixty-eight seconds and Six hundred and sixty-nine, Senku fell asleep.
Byakuya smiled fondly, bringing the covers up just a tad bit more. Carefully, he draped his hand over the teen and smiled to himself, ignoring the future in favour of reveling in the warmth of the covers and his son.
Just like old times.
That was the last time Senku, even if he wasn't aware of it at the time, felt the warmth of his father.
On the nights when Byakuya was out doing his astronaut duties, fifteen year old Senku counted himself to sleep in Byakuya's bed. He would never admit it, but on the days he felt especially lonely, he'd go over into his dad's room, and sleep in his bed. Like old times.
The glow in the dark stars somehow still up and running, even after nine, long years. He'd pretend he was curled up against Byakuya again, with the man's warm arm draped on him, his bushy arm hair, much like his beard, tickling Senku slightly.
Except this time, there was no warmth, just the cold memory that he was alone.
But, there was no logic in being depressed. Byakuya would return, and Senku could go back into his bed and not worry about frivolous things like loneliness.
Afterall, counting still gave him the comfort he needed, even if he never would admit it.
Encased in the strange green light (that looked oddly similar to the glow in the dark stars plastered on his father's ceiling), and his body suddenly going numb. As soon as his body was turned into stone, it was like his senses went dormant. His body was asleep, with only his mind awake. Alone.
The image of Byakuya's interview (could you really call it an interview if the man you were talking to takes your mic and takes it as an opportunity to gush about his son, not answering any of your questions, instead?) flashed in his head.
Would Byakuya be trapped in the stone too? Would Senku ever see him again, once he got out of this stone prison?
He decided not to give that thought any more attention, in favour of counting.
‘One.. Two.. Three..’
Despite logically, he knew that he wasn't feeling anything, Senku swore he could still feel the warmth of his father by his side.
Continuing to count, though this time once he reached four hundred and twenty-seven he refused the urge to succumb to sleep, and when he reached in-between six hundred and sixty-eight and six hundred and sixty-nine he didn't fall asleep. He almost felt proud.
I'm coming to get you out, dad.
(There was a ten billion percent chance he'd never see his dad again.)
When Senku finds Kohaku and gets taken to her villiage, he has a strong feeling he'd never see his dad again. It was likely. Ten billion percent likely in fact.
But he didn't face it, instead trying to be optimistic like Byakuya, not dwelling too hard on the facts. It's what he would've wanted.
(He's not coming back.)
The moment Senku's arm is brought up in the air by Kokuyo and it is announced that Senku would be the new chief of Ishigami Village, he knows that his theory the truth was true.
Even while the villiage applauses him and everyone stares in celebration, Senku can only think of his father. The one thing Senku tried to stay ignorant too, finally showed itself.
(He knew all along. It was only matter of time.)
The rest of the day is a haze, and Senku distracts himself with everything. From marrying and divorcing Ruri faster than you can say Doraemon ten times fast to Senku dragging Kaseki along the bridge, followed closely by Kohaku lugging massive barrels of alcohol over her head and somehow running faster than him. (Not like that was a massive feat anyway.)
He works his ass off finishing up the Cure-All Sulfa drug and giving it it's finishing touches, not even sparing a thought to his now officially-late father.
Physically, he's not alone. With Chrome's loud snoring filling up the room, how could he ever think he was?
But, mentally, he was.
His thoughts were going haywire, and Senku suddenly gets a wave of nostalgia from his days being six years old.
Staring at the dark, empty ceiling, he feels another wave of nostalgia, though this wasn't as violent as the previous, remembering the glow in the dark stars that he use to love.
Senku starts to count aloud, not sparing a thought about his volume. (Afterall, with how deep of a sleeper Chrome was you could pop a firework in his face and he'd keep snoring on).
“One.. Two.. Three..”
It doesn't give him the comfort it used to.