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Byakuya never thought that Senku would be the affectionate type, after all, Senku never showed any affection to him. He had never believed that love could get you anything in life, he had only ever been focused on science and research. Every date Senku had ever attended due to pressure from his friends, had never ended well, Senku had always been cold to the person he had been forced into seeing. So it came much to Byakuya's surprise when he walked into his house after his space trip, to see Senku lovingly engaging with a slightly familiar stranger lying across his lap.
Considering the lack of warmth Byakuya had seen from his son over the years, he decided not to make his presence known and to observe the strange scene unfolding before him.
"Senku-chan, why are you so interested in science? Especially when I'm right here, and I believe I'm much more entertaining than whatever you do in the lab." the stranger on Senku's lap spoke.
"Science is all about research and experimenting, mentalist. I'm sure you and your 'social experiments' can understand why I'm so involved with science." Senku began, "besides, who says I don't make time for you, I'm in the lab a lot less than I used to be since I met you, you're just as much of an important part of my life as science is."
"Fine, I guess I can live with that. I'm not particularly interested in science, but maybe you should teach me a few things, Senku-sensei~" the stranger teased.
Senku's face went red, very red, this was an unusual sight for Byakuya. With Senku's usually limited emotional reactions, this was definitely not one he had seen before.
Everything about what he was observing felt strange for him to see, he would have never have thought that the day Senku cut into his science time for another person would ever come. And he had most definitely never imagined that Senku would tell someone that they have as much of their heart as science does.
"Senku-sensei??" Senku blurted out, obviously startled by the use of the nickname "mentalist, you sure know how to bring out my emotions. You should feel proud, you're the first person I've ever dated, let alone the first person to get any type of emotional reaction from me. You're definitely special."
"Awe Senku-chan, you're cute, I'm glad you think I'm special, it means a lot to me, really." the familiar man had spoken once again, but Byakuya was still having a hard time placing him.
"I'm cute? You're kidding yourself, you're the cute one here, you and your stupid two-toned hair, I love you, dumbass." Senku had slightly rambled at the mention of being called cute, a light blush spread across his face.
"I love you too, science freak. I'm grateful you made room in your life for me, you're amazing and I can't wait to spend my life with you." the stranger had spoken again, he had a very sincere tone, although flustered.
As Senku was leaning down to kiss the man on his lap, Byakuya interrupted, knowing Senku wouldn't be pleased if he witnessed a kiss.
"uh... hello?" Byakuya started after clearing his throat.
"Byakuya??" Senku was shocked and immediately sat up pushing the man off of his lap.
"Wow Senku-chan, so cold, even after we exchanged our words of love!" the man stated, obviously being overdramatic on purpose
Senku's face flushed at what the man had said and he wondered if Byakuya had heard the whole conversation. "I thought you were staying at the base for a couple of weeks after landing? Why are you back?" Senku frantically tried to direct the conversation in a different direction, which, to his disappointment, did not work.
"I wanted to see you, I thought you might have been lonely but clearly not." Byakuya replied, laughing slightly. This comment made Senku's face flush an even brighter red.
"I- He's my friend, ok? I'm allowed to have friends." Senku rushed out, stumbling over his words.
"Wow Senku-chan, again? You're really cold to me today. I guess I should just introduce myself." the man spoke, even more dramatically than before. "Hi! I'm Asagiri Gen! And your apparently heartless son over there is my boyfriend!" Gen introduced himself with a smile on his face, proud to be in Senku's life. Senku on the other hand, hid his face in his hands, trying not to face the reality that was his emotions.
"Nice to meet you, Gen! I'm Ishigami Byakuya, I'm also Senku's adoptive father, although I'm sure you probably already knew that." Byakuya replied, a bit of uncertainty in his voice directed towards the man standing before him. "I feel like I know you from somewhere- I can't quite place-" He suddenly cut himself off and immediately switched sentences.
"Wait, hold on, are you the Asagiri Gen? As in the famous magician Asagiri Gen?" Byakuya had the sudden realisation in his mind that his son was dating a famous magician. His son, a scientist, dating a famous magician. It made no sense to Byakuya but he decided to let them have it and not question them.
"Ah yes, I am, I'm honoured you know me. I can't believe Senku-chan didn't tell me you were my fan. How upsetting." Gen answered, feigning sadness.
"Ugh yes ok, we get it. Byakuya, this is Gen, my boyfriend, I know what you're going to say, and get over it. Gen, this is Byakuya, my father. Ok good, you're acquainted now? Got it, now let's never talk about this again." Senku quickly interjected before Byakuya could answer, trying to avoid everything that was going on in the conversation.
"Awe, Senku, are you embarrassed? That's ok, I've just never seen you show this much emotion before. It's revolutionary." Byakuya teased Senku on his emotional display and continued on, "but seriously, Senku, I'm happy for you. I've never seen you this happy and comfortable with someone, not even me! I'm very glad Gen makes you happy and I'm even more glad that you found someone you're able to love just as much as you love science."
Senku's face went red for the millionth time that night, realising that Byakuya had heard every word in their exchange earlier. Gen, on the other hand, thought this was cute, and despite Byakuya being there, kissed him and shocked Senku to his core, and although shocked, Senku made no movement or hints that he wanted to pull away. Byakuya smiled at the interaction, knowing just how happy Senku was with Gen to display his emotions like this for everyone to see. He was truly grateful that his son was able to find someone who loved him to his core, despite not understanding half of the words Senku utters about science. He was even more appreciative of the fact that Senku had finally felt comfortable enough with him to share this sensitive part of his life, and he hoped Senku would grow more comfortable with him as time passes.