I doubt it was because his body was already used to it after a while time, but maybe because he knew what to expect; Mizuki was completely unrestrained - to my unhidden joy.

Moving his hips eagerly along with my movements, he had his legs wrapped around my waist and arms over my shoulder, already leaving shallow marks with his teeth and fingernails. 

Passionate moans echoed through the room, louder and more frequent once his body had eased up again.

I breathed in his scent - a mix of sweat and lust - while rubbing my lips over his neck.

Breathing was hard, thinking was hard. At least I didn’t have to hold back; even if I was slightly rough, it only resulted in him clenching tightly around me, causing my body to shudder in delight.

“Ah- nhh… ngh… Haah...”

He groaned right into my ear, gasping for air, then dug his fingers into my back. I slowed to let him speak, already aware that the movement had been done on purpose.

“Back… hurts… position- Ah!”
A shout of pleasure escaped his mouth mid-sentence, a deep thrust hitting him on a sensitive spot.

I had trouble caring about his words at that single moment, not with how he was wrapping around me and screaming out in pleasure. At least not unless they were heavy complaints.

His soft insides welcomed my increasing speed, his body rocking against mine.

He came faster than me - the dirty, suggestive sounds of our connecting bodies barely audible under his coming orgasm.

Biting my lip, I forced myself to stop for a while. I couldn’t come yet, I was still hard inside him and just waiting for him to give me the okay to continue.

The seconds passed dreadfully slow, so I, impatient, began to nibble on his ear and grope his ass in an attempt to arouse him again.

A successful attempt, thankfully. It didn’t take long for him to begin to squirm, the muscles around me inside him tightening and loosening several times.

“Another position”, he forced out, lust and excitement dripping from his seductive voice. I hummed, barely managing to listen to his words.

“Internet said doing it from the back is easier”, I commented. The internet said a lot of things, but that was certainly something that I would approve of. And it would be worth the painful wait for him to recover.

He cursed. 
“Fuck, isn’t that too shameful!”

“I’m working on it”, I dazedly replied to the first word, earning me a scratch. What had he expected? There weren't many positions that weren't embarrassing in some way. His earring had already warmed under the movement of my tongue, glistening with saliva. “It’s just me here, is there anything to feel ashamed about?”

After all, didn’t he allow me to touch him without restrictions? Didn’t he allow me to hear his moans, see his face when he comes? Didn’t he voice his preferences to me and let himself be mounted by another man?

Compared to that, was this change of position really worth any shame?

He halted, probably coming to the same conclusion.

Then his arms turned to push against me and I pulled out of him, instantly missing the restricting, hot walls of his body and eagerly throwing him around.

Mizuki gasped in surprise, then glared up at me. I leaned over him, stroking his waist and hooking my hand around his thigh to tug at him.

I liked that position. A lot.

One reason was that his approval was stroking my ego. Let’s be honest about that.

Another was that I was coming to enjoy biting him lately and the angle was just great for nibbling at his neck without coming close to any dangerous areas like his throat.

It was also easier to hold, as I didn’t need to carry his weight and, most of all…

“Yaa!”

He made a sound somewhere between a surprised squeal and excited moan when I mercilessly filled him up without waiting for another second, only my right hand steadying my body. 

My left was, in the meantime, snaking around his hip to grip the twitching part on his front.

“Don’t-”, he started, then couldn’t continue anymore. Between the hard thrusting rubbing against the most sensitive parts inside him and my hand pleasing his front, he let his upper body collapse into the pillows without strength.

“See, it’s a good position”, I whispered into his ear, then sucked in a breath when he tightened around me.

“A-uh… Ah, ahn-”
The inarticulate response was a set of moans accompanying each thrust and stroke.

Tonight, I wasn’t going to let him off easily.

The night had been long so the system waking me with an irritating beeping in my head was very unwelcome.

My body felt sticky and actually rather disgusting, but the warm body placed snuggly against mine was worth ignoring all discomfort from not having cleaned up.

I hadn’t had any energy left in the end. After refusing to let him come for a while I could drag out the time I could continue for quite the while. By the time we were tired out, I didn’t want to move another inch.

The bathroom was too far away for me to carry both of us over, wash up, then change the bedsheets and lie down again. We had just stayed right where we were.

Moving my fingers just the smallest bit, I brushed them over some stray strands of Mizuki’s hair in a daze.

So weird.
To have a boyfriend, weird. To have it be him, weird. To go all the way, weird.
It was all just weird.

[This is the result of the host’s and the target’s chemistry. There isn’t anything weird about it.]
I don’t remember inviting you to my thoughts, but good morning.
If it hadn’t been for you, I wouldn’t be in a relationship with him, would I?

There was a short silence that appeared as if the system was hesitating.

[Not necessarily. There were a number of ways that you could have gotten acquainted and developed your relationship to this point.]
That’s… weirdly relieving to know. 

But in the end, where do you come from?
[Does the host truly wish to know?]
Yep.

[The host was chosen from the group of humans in a certain range of age, with homo- or bisexual tendencies and under consideration of the fact that the possible hosts shouldn’t have been in a relationship before and were in some way ...impaired to starting one. In your case, the impairment is your social awkwardness resulting in your not believing you could ever enter a relationship.]
...Soooo
I won the lottery.

[...]
[Yes.]
I can live with that quite well, actually. 

It’s fine with me.

[The host is very tolerant. It is suggested that you stand up now and begin to wash your partner, as it can be assumed that he will be quite sore when waking up and won’t want to move.]

Oh yikes, my family won’t be out forever. Does that mean he’ll keep on lying here?

Now that’s gonna earn me some awkward glances…

Moving together sounds even nicer now. We can just lounge the whole weekend, nothing hurrying me to stand up when I’d rather keep that slender figure in my arms.

Hearing someone else breathe slowly as they sleep is amazingly calming for me. It’s such a nice sound, so peaceful.

I burrowed my face in Mizuki’s hair and gave him a gentle kiss on the head. 
He shifted a bit in his sleep and sighed, so I waited until his breathing was back to its slow, even pace before untangling myself from him.

Owl

There's a "M" in the title, I assume that's enough of a warning. Besides, this was a shorter scene xD
Riku is getting comfortable in his role as a boyfriend <3 

Btw, we are very close to the end orz to think it would be over so soon... but there are extras coming (of different lengths) that will be nice for you to read

Mizuki's System's theater:

Riku: "I never thought I'd win the lottery some day"
System: [I'm glad it was you.]
Riku: "..."
Riku: "Don't make me cryyy QAQ"
Riku: "I'm an emotional person!!!"
System: [Yes. It's a sweet quality of yours.]
Riku: "｡ﾟ(*´□`)ﾟ｡"