This is a sort of prompt fill for an anon on my tumblr, who said- 'So I noticed you're taking nsfw requests for you MizuSei 30 day challenge and does Sei even know about sex? I donhink he would unless ViTri took advantage of him at some point when he was in Oval Tower.'

I was thinking about it and how much sense it made so much I wrote something for it, so it's not technically a prompt but yeah :P

"Aoba..?"
"Mm?" Aoba didn't look up from his coil as Sei spoke, confused pout almost obvious in his tone.
"What are they doing?"
Now he looked up, almond eyes landing on the TV screen, where the characters in the terrible romance film they were watching had begun to kiss rather heatedly. He glanced at his brother next, black hair being twisted round a finger as he peered at the screen with interest and maybe a little disgust.
"You're serious?" Aoba asked, lowering his coil with a sigh and rubbing his forehead as Sei just nodded, looking so innocent, which in all honesty he was. "They're kissing, Sei. You know what kissing is right?"
Sei looked indignant now, crossing his arms huffily. "Of course I do, like when you or Grandma kiss me."
Aoba's eyes met Ren's across the room, the other boy shrugging and pretending to be busy practising his letters so as not to be pulled into the increasingly awkward conversation.
"Um, not exactly. Well," he rubbed the back of his neck, feeling a blush grow on his cheeks. "That's kissing too I guess. But it's different to that."
Here Sei's eyes flashed back to the screen, where the male lead seemed to be trying to lick the females teeth, eyes widening in mild horror. "Yeah, I can see that. But.. I don't get it."
"Oh wow. Okay, so.. you kiss someone like that, when you like them." Aoba explained. He supposed spending your entire life locked up in a room completely blocked off from outside life was bound to lead to some awkward questions needing answers.
"But I like you, Ren and Granny." Sei argued, looking so adorably confused Aoba couldn't help but laugh softly. "Why don't we kiss like that?"
Ren focused on his letters intently, trying to pretend he couldn't hear the somewhat disturbing conversation going on just metres away from him. Aoba, meanwhile, visibly paled, laughing sheepishly and reminding himself Sei wasn't being weird, he just didn't understand.
"Because we're family, and it's illegal, not to mention weird to do things like that with family."
"Ren isn't technically related to us, and we were made in a lab." Sei reasoned, and Aoba found himself wishing that argument didn't make so much sense.
"Yes, but you don't have to be blood related to be family." Sei nodded at this, and Aoba sighed in relief. "When I said liking someone, I meant.. romantically."
"Romantically?" Sei looked just as confused, biting his lip nervously as he glanced at the screen, which thankfully was now on an advert break.
"Yeah, like me and Ren." Amber eyes met almond at this, smiling softly across the room. "You'll meet someone, and you want to spend all your time with them. You'll think about them a lot. They might be funny, or really nice, and you'll feel.. comfortable around them."
"Someone special to you, who makes you happy every time you see them or think about them." Ren chipped in, having given up on writing the alphabet and decided to help Sei instead, a much more worthy cause.
"Hmm," the black haired boy was silent for a moment, thinking about this, before a small, almost love-struck smile appeared on his face. "Like Mizuki?"
"What?" Aoba remarked almost instantly, eyes widening in alarm, being met with a worried look from his twin.
"What?" Sei replied just as fast, eyes looking panicky as he noticed Ren's surprised expression and Aoba's outright shock.
"You.. do you, like, Mizuki, Sei?" Ren spoke up, seeing as his boyfriend was too busy trying to catch flies in his open mouth, or perhaps buses with how slack his jaw was.
"Well, I don't know, I guess?" His fingers writhed in his lap uncomfortably as he looked from Ren to Aoba. "Is that okay?"
The bluenette seemed to have finally found his tongue, smiling as he overcame his surprise. "Well you can't help who you like, that's one of the worst things about it."
"How?" After a pleading look from his boyfriend, Ren came to sit beside the twins on the sofa, arm loosely around Aoba's shoulders.
"If they don't like you back, or if you're not brave enough to do anything about it, it hurts." Ren was the logical choice to answer this, having loved Aoba for years as his allmate and yet been unable to do anything about it, watching as Sly Blue had meaningless flings and Aoba made new friends.
"And even if they do like you back, and you're together, it's not always easy."
Sei pondered upon this, watching the way Ren played with a strand of blue hair and Aoba snuggled into his hold, feeling a pang of some unfamiliar emotion in his chest. Maybe jealousy.
"Is it worth it?"
Aoba didn't even need to think about it, squeezing Ren's hand where it rested on his thigh and smiling as it squeezed back, "yeah, definitely."
Ren nodded his assent a minute later, wondering just what Mizuki might have in store.
"So.. if I like someone, I should kiss them?"
"Not right away." Ren answered, almost sensing Aoba's disbelief and growing impatience. "You should do other things first, maybe hang out as friends for a while. Go on dates, hold hands, hug, that kind of thing."
"Oh, okay."
"Maybe you should just let the other person take the lead." Aoba suggested, deciding that was a far better choice than letting Sei run wild kissing people he liked. "Did that.. answer your question?"
Sei nodded slowly, "yeah I think so, thanks guys."
They both muttered something along the lines of it being fine, Aoba making a mental note to subtly prepare Mizuki for what might be coming the next time he saw him. The sound of soft, almost pornographic moaning from the television made all the blood fade from Aoba's face, stiffening in Ren's hold as Sei blinked blankly at the screen.
"Aoba.." Sei began, not aware of his twin silently pleading for him not to ask. "What are they doing now?"
"Ren, would you like to explain?" The bluenette tried, voice shaking with horror and amusement as he heard the breath from beside him hitching in annoyance.
"I- I think it would be better for his brother to tell him." Ren stammered, deciding to murder Aoba later for trying to leave him in such an uncomfortable position.
"Sex, Sei, they're having sex." Aoba remarked, having lost all ability to care by now and fully prepared for the barrage of horrifying detailed questions that would be coming his way.
Sei nodded, seemingly understanding as he continued to stare at the screen where the characters were writhing together. "What's sex?"
That was the final straw for Aoba, who stood from the sofa, arms held up in defeat, "Right! I give up, I'll buy you a book Sei."
With that, he stormed from the room muttering about ridiculous questions and stupid movies and useless boyfriends, Ren smiling apologetically at Sei before following, leaving Sei wondering just what help a book would be.