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English
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Published:
2025-05-04
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1/1
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Should Have Knocked

Summary:

Byakuya gets the shock of his life when he arrives home early one morning. After months in America he'd been excited to catch up with Senku. He didn't expect to be partially traumatized when he went to wake him up.

After all, who would expect his romantically oblivious son to have an actual person in their bed???

Notes:

Hello! Hope you're all well. Here's a silly little idea I had after re-reading the manga for the second time in a month. Help, this fandom has corrupted my life. ^_^;

(Note: Senku is eighteen here and Gen is twenty-two)

(See the end of the work for more notes and other works inspired by this one.)

Work Text:

Byakuya let out a happy sigh as the apartment building came into view. Home. Living in America for so long he’d almost forgotten the warmth seeing one’s own home brought. A place where all his dreams stemmed from. Planning for his JAXA application to planning for a trip to space, all of it began here. The place where he’d raised one seriously precocious kid into a confident maniac of an adult. What wonderfully weird memories those walls contained.

Speaking of his crazy son, Byakuya couldn’t wait to see Senku. The phone calls and random visits -the eighteen year old still liked to mooch off his money- just weren’t enough interactions for Byakuya. He and Senku might not have the closest relationship, but Byakuya still wanted to know what was new in his life. Like was his senior year going well? Had he made any new friends? Was he dating?

He snorted. Right. Senku only loved research projects, astrophysics, and experimental chemistry. His people skills were nil (how Taiju and Yuzuriha put up with him all this time was a mystery). A pretty girl could waltz right up to the boy, confess her love, and Senku would only list off the chemical composition of her hair spray without missing a beat. That’s just how he was. Byakuya long gave up on Senku ever forming any meaningful romantic relationship.

Too bad, really, Byakuya sort of wished for future grand kids.

He’d just have to do with getting to know his son better then, and because it was Senku, he’d get any new information through flat facts with little to no emotion or an entire lecture about keeping his nose out of his business. Eh, he figured either would be fine. It was a start.

When the cab drove off he hauled his lone suitcase up the stairs with a cheerful whistle. A cute dog dashed by his feet and he grinned at the small girl chasing it. Ah, youth. What a beautiful thing. Maybe he’d greet the neighbors another day. Might be fun to have friends on this side of the world.

He noticed with amusement after coming inside that nothing had changed. NASA posters hung on the walls, the bookshelf was cluttered with science magazines. Byakuya’s collection of model rockets still lined their custom built shelf. All dusted. He’d have to thank Yuzuriha later for taking care of the place.

Only a clean set of white trainers alerted him that Senku was home. As it was still early in the morning, Byakuya quietly snuck by the ‘Caution- Science In Progress’ sign on Senku’s door and put the suitcase away in his own bedroom. The bed was neatly made and the air smelled strongly of sweet laundry detergent. Seriously, they didn’t deserve a girl like Yuzuriha as a friend. Taiju better have confessed to that gem already before someone else had snatched her up.

Senku never slept past eight and it was already seven-thirty, so he had some time to relax on the couch. Any minute now and Byakuya could obnoxiously greet him in the loudest, most annoying voice he could manage. Being his dad meant Byakuya reserved the right to drive Senku crazy. It was part of the job description.

The clock ticked by eight. Then eight-thirty. Then closed in on nine.

Huh.

“Bet he stayed up all night on a project,” he muttered with slight fondness. Better go check on him then, make sure he hadn’t blown himself up or choked on noxious fumes. Wouldn’t be the first time either happened.

As silently as possible, Byakuya slid Senku’s door open. No smell of gas or sulfur, excellent sign. Senku’s face was tucked into his pillow, his mouth letting out soft snores. Only in sleep did Senku look like a normal kid, no confident smirk or deviously excited grins. Byakuya smiled for a moment. He loved the science genius but sometimes this side of Senku was nice too.

The smile lasted less than half a second, replaced with an open mouth look of utter shock.

There, snaked over Senku’s side, was an arm. And now that Byakuya finally took a good look, that arm was draped over Senku’s very bare chest. A bare chest sporting a round bruise, actually no, several round bruises. Bruises that sported small red teeth marks.

There was a girl in Senku’s bed.

All Byakuya could make out of her was the arm and a hint of white hair. Her body was tucked right up onto Senku’s back, not even her face showing. A blush spread up Byakuya’s face at the obvious facts laid out in front of him. Apparently his son had more game than he let on. Byakuya didn’t know whether to feel proud or grossed out. Maybe both.

He must have let out a surprised sound at some point because Senku rolled his head off the pillow as bright red eyes blinked open. A whole spectrum of emotions flashed on the teen’s face; confusion, recognition, shock, and finally straight horror. Senku tugged the blanket tightly over himself and sat up with the brightest blush Byakuya had ever seen on anyone in his life.

“Dad!”

“Sorry! I’m sorry!” Byakuya slowly began to back up. “I’m just- I’m just going to make some coffee. Ah, take your time. No worries. I-” He fled before anything else ridiculous fell from his mouth.

The coffee pot trickled away in the tense atmosphere. Byakuya sat at the table and tapped his fingers along the wood with anxious anticipation. Senku and his date would have to pass right by him if they wanted to leave the apartment. He wondered if this was a good time for the talk. Senku may be eighteen, but as a dad Byakuya was expected to make sure the kid was safe. Right? Right.

Ugh, this was going to be soooo awkward…

Cautious footsteps padded down the hall. Senku appeared around the corner, now dressed and hair hastily brushed. A figure in a purple hoodie hid behind him. Byakuya spotted a splotch of dark hair mixed in with the white. Senku was obviously trying to play it cool, but his twitching fingers betrayed him. Poor kid. This had to be the most embarrassing thing that would ever happen to him.

“Um,” Senku started, then cleared his throat. “I didn’t realize you were going to get here so early.”

“An earlier flight opened up,” he replied. “Thought it’d be nice to get home early.”

Senku rubbed the back of his head and scrunched his face up in displeasure. “Um, look, this isn’t going to be easy for either of us. You want to go ahead and rip off the band-aid and get it over with? Ask the questions and we can move on with our lives.”

Byakuya snorted. “Straight to the point, as always. Alright then.” He clapped his hands together, startling the person still hiding in Senku’s shadow. “I suppose I’ll go with the obvious one- who are you and where is my romance impaired son?”

Senku’s eyes narrowed. “Ha, funny. I forgot how witty your humor could be.”

Byakuya grinned. At least a bit of the tension cleared up. “Fine, fine. Who is this lady and how did you manage to convince her you’re not a complete mess?”

There was a long pause. Senku glanced behind him, lips falling into a concerned frown. His fingers twitched more and Byakuya was amazed to see the smallest tick of actual worry in those red eyes. What could make such a confident man so uneasy? He should know Byakuya wouldn’t be angry at him. Byakuya scanned his mind for an answer but came up blank.

“Dad…” Senku paused to scrub a hand over his face. He took a long breath. “You’re misunderstanding something big here.”

“Am I?”

Senku nodded. He took another pause before taking a slow step to the side. Finally his mysterious partner appeared clearly. Pale cheeks were flushed under the purple hood. Black and white hair poked out choppily. They were thin, taller than Senku, and obviously very, very-

Male.

“Oh,” Byakuya slipped out. “Oh.”

The strange boy sheepishly raised a hand in greeting. “Hi, Ishigami-san. This definitely isn’t how I wanted us to eet-may.”

Senku’s lips quirked in a fond smile for a split second but it fell when he turned his attention back to his dad. His shoulders tensed uneasily. “This is Gen. My boyfriend.”

“Oh.”

“Do you know any other words, old man? The broken record isn’t helping the situation.”

Byakuya tried to form words and failed to find something to say. Alright, he could do this. His only kid just announced he wasn’t quite straight. Gay, pan, bi, whatever. Senku always took the harder route in life, whether it was declaring he was going to the moon as a young kid or applying to every prestigious tech university on the planet. The man lived and breathed challenges. This was just the next one in a very long line.

And his dad never once let him down on helping him overcome those challenges. Senku wanted to learn science? Byakuya filled his room with every scientific gadget he could get his hands on. Wanted to fly to Africa for a field study? Byakuya bought the tickets without hesitation. That’s the dad he was and had always wanted to be.

Now Senku presented with him with the next big parental obstacle. Dating the same sex in a conservative country wasn’t going to be easy. People were still cruel. Just because Senku was intelligent didn’t mean they’d give him a break. Senku would be a target for the rest of his life to those homophobic assholes. And damn it, Byakuya was going to do his damn best to help protect him.

He finally cleared his throat. “Senku, you know I support you with everything you do. I’m never going to stop. I’ll be dead and gone and still haunting your ass to make sure you eat and sleep.”

“Yeah?” Senku cracked a smile and Byakuya was pleased when his shoulders relaxed. “Ghosts aren’t real. If your electric afterimage does come for me I’m grounding this whole damn apartment. Enjoy being eternally evicted.”

“Senku-chan, that’s so mean!” Gen whined out. His hoodie’s sleeves were a tad too big and he batted Senku’s shoulder with the end of one.

Senku shoved a pinky into his own ear with a snort. “Doesn’t matter. An impossibility is an impossibility. Besides, I think our current situation is a tad more important than phantom idiots.”

Gen smiled awkwardly. “I suppose you’re right.” He caught Byakuya’s eye and that smile faltered. His hands slipped inside those over-sized sleeves as he leaned into Senku’s side. Anxious. Lost. Scared.

The oldest felt a pang of guilt. It wasn’t just Senku he had to reassure here. “Gen, huh? You don’t need to be worried. Senku has a knack for surprising the hell out of me. The dumbass could have least given me a clue before this.”

“Didn’t seem relevant,” came the dry reply.

“’Didn’t seem relevant’? Seriously?” Byakuya let out a laugh. “Idiot. I’m your dad, this sort of thing is always relevant. How else am I supposed to plan ways to embarrass the hell out of you in front of your boyfriend? I won’t have any good anecdotes for at least another hour.”

“How tragic.”

Byakuya stood to grab his cup of coffee. “Yeah yeah. Your old man never thought anyone would actually have the patience to date your anti-romantic ass. Gen, if you run now I promise to hold him back.”

Gen cracked up while Senku huffed. Any tension in the room vanished. Byakuya paused as a wicked idea popped into his mind. A devious grin to rival Senku’s spread over his face. Time for a good ol’ dad attack.

With all the casual grace he could muster, Byakuya leaned back on the counter and coolly took a sip from his mug. Senku’s eyes widened in realization and he grabbed Gen’s hand as if to flee. Oh no, not a chance, kiddo. Byakuya was just getting started.

“Do I need to buy some condoms?”

Senku stomped off with a hysterically laughing Gen behind him. Byakuya smiled around the rim of the mug and let out a happy sigh. Yep, being back home sure was nice.

Notes:

Thank you for reading! Please leave a review if you want. I eat them as snacks and lately I've been starving. O.o