She can't actually channel enough mana all at once to make someone come in moments. And she's not as experienced as some of the real experts out there...

What she can do, is make sure her own pleasure is obvious, and maneuver him just so, so they can push together more easily. Her tentacles wrapped around his waist and hips help push him in and out of her slick tightness. Her breasts press against him, and she moans into his ears and rubs his back and it won't be surprising if he comes in short order.

As he does, she ramps up the pleasure as much as she can with her capacity, making it last a good bit longer. Then trail down to almost nothing, holding a gentle resting pose for a bit, rubbing circles into his back and just holding his dick inside her without moving so there's no painful overstimulation.

"How are you feeling? More, again?"

"Please, take me further. I've never felt like this, you're beyond fantastic oh, oh oh wow..." His enthusiasm is very obvious.

She blushes and grins. "It's amazing, isn't it? I'm glad. The joy of service is great." 

But... Hmm. If there's nobody else here with access to sex magic, going too far could be a disservice. Also, she can't actually channel magic all day.

She starts a slow gentle grind again.

"I can't go much further. Just, different further. And my magic will get tired. Do you want to be... Bigger and feel touch more?"

"Yes, I want to try it. I want to feel... totally new things to feel." He looks at Bysellia, pleading.

"Okay. I think we should get out or sit at the edge for a moment so you can see it happen. I'll use my breasts, and my mouth again."

Guys like variety, and using her mouth is hot, and oversized phalli are hot too.

She starts gently tugging towards making this happen, lifting him gently off her.

He follows Bysellia's commands, starting to make his way to the edge of the tub. He chooses to sit with his legs inside the warm water of the tub, as he looks on at Bysellia with curiosity. "See it happen? You're making me curious, here."

Smirk. She wraps her hands around his dick and gently strokes.

Once more incanting, though the last syllable is different this time.

And it gets bigger. From her hands mostly covering it, it slowly expands to a monster of a cock a foot long and just as girthy in comparison. It also becomes more sensitive, feeling her hands rub up and down and the warm water surrounding it with greater intensity. It doesn't feel uncomfortable, it feels completely natural.

Bysellia licks her lips and stares at it with undisguised lust. She presses her breasts against him, one hand gently massaging just under them, the tip just below her mouth.

He responds with an immense amount of anticipation obviously visible on his face. "Can - can - can you use the mouth guard this time, please? I just like - the symbolism of it, the way it's saying just", he catches his breath, "I'm not rejecting you and don't feel any need to defend myself or close myself off from you and know you won't violate me in any way."

"Ooh. As you want~"

Where did that thing go? Ah, it's still on the couch in the other room. That's okay, utility magic can summon it. She has to drop the sex magic for a moment to do that, but the effect lasts long enough for her to refresh it once she has the mouth guard in.

"This is really nice. I feel safe and liked, and you can use my mouth however you want."

Lick.

He stops thinking entirely, grabbing Bysellia by the head and shoving himself all the way down her throat, quickly and roughly moving her head without a care in the world as he tries finding her limit and turning her mouth and throat into a toy. He uses whatever concentration he has to try feeling whether there's any hint of resistance or discomfort on Bysellia's part, as he forgets about the world and his consciousness gets consumed by the pleasures of the moment.

It... Is actually a little uncomfortable, to be treated so roughly. Not physically, but mentally. Physically, the mutation of her throat makes this throat-fucking pleasant enough that she actually builds up to an orgasm thanks to her previous arousal.

But it reminds her of unpleasant things. Just a bit. Even though she chose this one and made the offer, expecting an oversized intrusion. Thus there might be a few hints of discomfort if he gets especially forceful or grips too tight. But this is obviously something especially pleasing, it's important, so she does her very best to sink into the moment and, instead of just not showing discomfort, to actually be comfortable, basking in raw sensation and in service instead of bad memories.

She's disciplined and determined, she can take it. Her throat is a tool of pleasure and service. The bare hints of discomfort remain just tiny hints, possibly missable, and vanish after a bit.

And then she can savor his taste again, and climb up to embrace and massage him gently as aftercare, humming softly.

After asking Bysellia to use her powers to make the two of them dry, he walks over to his bed, lying down and enjoying Bysellia's touch for a while, under the thick and warm blanket.

"I think the world should hear about you. About how amazing, and how beautiful, and how caring, and how skilled you are. I think you're a real treasure, someone who's here to make life better for everyone. Don't forget that." He smiles at Bysellia, embracing her with all of his body. "Now, although all those thing are true, and I want to be able to enjoy your touch forever... I'm not ready to have you sleeping, here. I think you should go back to talk to Cynthia about everything that's happened. And to talk about what lies in wait for you."

Yeah.

In a lot of ways, literally sleeping together is a whole other level compared to 'merely' having sex.

And seeing the way it happened here, with a whole new set of assumptions and norms... This world doesn't need to be exposed to all of her home. Just some of it. Just the parts that can help each other. She has a lot to pray about, and get her thoughts in order about, now.

"I'm really happy. I- My whole life I wanted to be good for people, but be able to choose it. And help people, in good ways. Now I can. So thank you for letting me in this much. There's going to be more... But I'll talk to Cynthia about it." 

One last hug. "Do good with your robots!"

She will figure out where her clothes went, put them on, take the elevator down, and unhurried walk back towards Cynthia's tower, watching the city as she goes.

It doesn't take long before Bysellia finds her clothes again. The walk to Cynthia's house is also quite brief. Taking the elevator up, she finds herself in the main room, seeing Cynthia wearing nothing at all! ... or that's the illusion she gets, until she realizes that she's unable to see Cynthia's lower lips. She's not sure why she's looking like that, at the moment. 

Semi-nudity is not actually noteworthy or surprising to her on a gut reaction level. It's a little surprising on an intellectual one.

"Cynthia! Today was great! Thank you so much again! I actually have some questions if now is good to talk?"

Oop, wide stance. Wide stance. She spreads her arms and tentacles, offering a hug.

Getting a closer look reveals that Cynthia is wearing a set of panties, and a bra, that matches her skin tone very, very closely. Cynthia leans into the hug.

"I'm happy to talk, yes. What are your questions?"

"Oh wow, I have a new one, how can I get one of what you're wearing? But also, I think I don't know how money works here. We used shiny circles back home. How does it work?"

"We can go back to the tailor that we bought your clothes at, they're underwear specialists and they stock underwear just like this and many others. Oh, and money works by using phones. We can send money to other people with phones. And the money is kept in the phone-card, the card with all the data that's built into the back of your phone. So you don't have to worry about the battery wearing out, or anything."

"So I need to get a phone?"

She ponders, mid-hug.

"I don't think I know what robots and phones and data and batteries are just from hearing the word..."

"Yes, that you would probably need. They're unbelievably versatile devices, they're really amazing that way." Cynthia starts nuzzling Bysellia, as well as moving her hands lower along her back, during the hug.

"You might have better magic than us... Robots, phones... The thing we rode in, and great clothes..."

"Well, none of it is magic! It is very clever. And some say that human brilliance is magic in its own way, but that's just abusing the word in silly ways."