Chapter Text
Ishigami Byakuya was not a religious man, but with Senku sitting on his lap leaving small marks on his collarbone, he could only think that if there was a god watching at that moment, it was better for him to look away.
"Senku, we can't continue with this, we shouldn't continue with this," he murmured with a deep voice, clinging to the last shreds of reason he had, yet he couldn't move the young man from his position as if he were a bomb about to explode.
"And why not?" he questioned, slightly furrowing his brow as he wiped away the thread of saliva that had formed between his lips and the older man's jaw. "You constantly complain about my lack of affection towards you, and analyzing your particular physical responses..." He observed his father from head to toe as if he were a personal project that required his utmost attention. He smiled confidently upon noticing his ragged breath, the blush on his face, and the growing bulge protruding from his training uniform. "...I can deduce that I am doing an excellent job, although I can do even better." He got up from his lap with some difficulty and knelt in front of him, feigning false innocence in his crimson gaze.
"What... what are you planning, Senku?" Byakuya asked, still unable to regain his composure after his ten-year-old son had marked him in strategic places.
"Isn't it obvious? I've heard you fantasize about this since I can remember and how lately you've been behaving well..." He began to slowly unzip his uniform.
"N-no, wait, Senku," he stopped him with his right hand without exerting much pressure on him. Senku did like to see that side of him, so vulnerable and needy, different from the confident and playful old man he always was. The best part? That view was only for him.
"Do you really want me to stop, Byakuya?" he ran his small hand over the fabric of the crotch, enjoying his reactions. "Wouldn't you like my virgin mouth to be filled with your semen?" He felt a hundred billion percent like a cheap whore saying that out loud, but according to his research, those kinds of things excited old men like him, surprisingly, it worked.
Byakuya laughed upon hearing him, causing a blush on the young man's cheeks who looked away feeling exposed.
"Well, since I see that someone has made such an effort to make me feel good..." With his right palm, he cradled Senku's face to look him in the eyes while his left hand finished unzipping his uniform and partially freeing himself from his boxers. "It would be a waste not to test your hypotheses." He kissed his lips without warning, allowing the younger one to explore every corner of his mouth without pressuring him as he waited for him to get used to the level of intensity. When they separated due to the need for oxygen, Senku took a few extra seconds to observe the erection in front of him. He had an idea of the size, but seeing it in person was completely different.
"You don't have to do it, Senku," he declared softly, stroking his hair lovingly, although internally he just wanted to fuck that little know-it-all mouth once and for all.
"Don't underestimate me, old man." With determined and somewhat trembling hands, he began to stimulate him from the base to the tip. At first, his movements were clumsy and lacked rhythm as he was experiencing sensations completely beyond his understanding, but he was willing to go all the way. When he felt it was time, he took a breath and introduced Byakuya's length into his mouth. Due to the speed at which he did it, he triggered a gag reflex, causing the older man to chuckle and help him clean the corner of his lips.
"Senku, you can't take it all in with one movement or you'll choke, you have to be slower."
"Tch! I know, don't bother me, I just wanted to try." He wiped away the remaining saliva running down his cheeks and this time he was more careful.
"...Like an ice pop, they said, an ice pop doesn't have three venous systems or is made up of three types of nerves."
As he thought about his anatomy studies, he didn't realize that he was increasing the pace of his movements exponentially until Byakuya's hand gripped his hair.
"Forgive me, Senku, I..." He couldn't finish his words and instead began to move his hips roughly until he fully inserted his penis into Senku's throat, who tried to pull away but his strength was not enough to do so. "Hold on... a little longer." Senku's tears began to trickle down his cheeks and that image made him ejaculate. Now Senku was on the floor trembling, breathing heavily, with teary eyes and covered in Byakuya's semen. He was so damn attractive that he felt he could ejaculate a second time just by looking at him.
When they both managed to catch their breath, Byakuya leaned towards him, ready to clean his face stained with white. "I'm sorry, Senku, I couldn't control myself." Senku snatched the handkerchief with false indignation and stood up.
"I'm not surprised at all, but if you do it again, I swear I'll bite you." After finishing cleaning himself, he discarded the handkerchief and stretched before heading to the exit. "Don't apologize, your card will make up for everything, you damn pervert." He commented with a smile and stopped at the doorway. "And by the way, don't use my absence as an excuse to mess with the idiot Shamil, if you try, he'll see the marks I strategically placed to form the initials of my name, so spare me the awkward talk about how your ten-year-old son excites you so much and stay away from him, understood?" He didn't wait for a response and walked away slowly but confidently. "Come back soon, old man, I'll be waiting."
He muttered to himself, satisfied with his work. Perhaps he would give him an even better reward when they returned from the lunar mission, if he came back with interesting gifts, of course.