This is an English translation of the original Japanese novel, processed through a translation tool.
There may be some inaccuracies.

Link to part 1
https://privatter.me/page/67d4f02a7a149

Alastor rhythmically moved the tentacle, vigorously stirring Lucifer’s insides.
"Ahh… ♡ S-stop, really, I’ll make weird noises… ♡"
"Then does truly feeling good turn you into the vulgar, depraved mess from the video? Did you know for certain you’d become like that because you’ve done it with your wife—or even someone other than me?"
"Nn! Ah… ♡"
"…Silence is as good as a yes, isn’t it?"
"Ah, ahh… ♡ I’m gonna, gonna cum… ♡"
"Lucifer… are you climaxing? Your insides are clamping down hard."
"…! Fu, ugh… kuhh!! ♡"
Lucifer’s body stiffened for a moment. Seizing the chance while he reveled in his climax, Alastor slowly withdrew the tentacle that had been tormenting his insides. In its place, he pressed his own engorged member against Lucifer’s trembling buttocks and thrust it in fully, without restraint.
"Agh?! ♡ I just came… ah, aahh!! ♡"
…Lucifer’s moans were growing closer to those in the video.
The strained, crushed sounds spilling from his throat under sudden stimu,ation—it seemed that only rough treatment could draw out such noises.
Still not enough, you filthy wretch?
His low, ragged breaths turned into beautiful, hoarse, saccharine moans as they broke apart.
…Those sounds still lingered.
The words Lucifer had screamed in the video, calling out for him, wouldn’t leave Alastor’s ears.
"I’m cumming! Again, again…!! ♡ W-wait, ha, it’s too much, too intense!! It hurts, it’s painful… ♡ Stop, please stop…!!"
"Lucifer… do you want it or not? I can stop if you really mean it. But with your insides gripping me so tightly, I can’t tell if your protests are just words or if you genuinely hate it."
"I don’t want my voice, my voice to come out!! I don’t want you to hear… such vulgar sounds…!! ♡ Wait… haa, ahh!! ♡ No, I’m gonna cum again…!! …!! ♡"
"Then admit it. Like you explained earlier—you turn into a shameless, vulgar mess when you truly feel good, don’t you? Even while being fucked by a man you despise. The moment you begged me to lend you my body, the you in the video and the you now became the same to me: a contemptible, lust-drunk degenerate. …You didn’t realize that, did you?"
"Ahh! Ah!! Aghh!! ♡"
"If you won’t admit it… I’ll stop right here. The you now is different from the you in the video—a proud King of Hell, right? You wouldn’t get lost in fleeting pleasure, fucked by a sinner’s cock. Isn’t that so…?"
As he spoke, Alastor slowly began pulling his member out of Lucifer’s insides. Perhaps unwilling to let it go, Lucifer’s walls twitched desperately against Alastor’s movement, but he ignored it and continued withdrawing. Just as the tip was about to slip out, Lucifer finally broke and shouted:
"I admit it!!!! I admit it!!!! Don’t… I can’t stand it without feeling good anymore…!!
I’ve always, always wanted someone to fuck me like this… to ruin me so completely I can’t think…!! It’s that video’s fault… seeing it made me realize what I truly wanted, and I couldn’t hold back anymore…!! I’m broken, I need it, I want it to take me, to surrender everything—the pain, the memories I want to forget, all of it…!!"
"! …"
Words poured endlessly from Lucifer’s mouth.
Stunned by the sheer intensity, Alastor could only stare at him in silence.
Lucifer moved his lips slightly, as if confirming his own words, then let out a quiet "ahh." Tears began streaming down his face as he broke into sobs.
As if something inside him had shattered, his eyes overflowed with tears.
Seeing this, Alastor felt deeply shaken.
He didn’t know what to do with Lucifer. He’d never seen him act so self-deprecatingly before.
"Hahaha… so this is how it ends… I couldn’t control myself… You get it now, don’t you? I’m someone who can’t suppress my desires. The same as the future me in that video. Nothing’s changed… And I can’t stop myself from dragging others into it. Even myself—I want to ruin everything… My rationality can’t hold back this desire anymore…"
"…That’s not what I wanted to hear from you…"
"…It’s the same, isn’t it? Whether the me now and the me in that future video are the same… They are, so I ended up wanting to rush to ‘that side’… Even though that exchange isn’t something I can handle alone. If it was going to turn out like this… I wish I’d never known. Never seen it. If it’s something I can never have forever, it’s just suffering. Not just for me—I’ve made you suffer too… Feel free to despise my selfishness. I have nothing left, no worth at all…"
"Lucifer…"
"…I can’t… do it alone anymore… It’s impossible… Help me… please… save me…"
"…"
Alastor hadn’t meant to deal the finishing blow to Lucifer.
But hearing those anguished words, he understood.
He had destroyed the last shred of rationality Lucifer had clung to.
…He’d seen his future self in that video—the self he truly wanted to become.
He’d discovered the "correct answer" he’d been chasing.
And that’s why he’d broken.
Seeing this, Alastor gently stroked Lucifer’s hair.
A shattered vessel couldn’t be restored, but he felt compelled to at least gather the pieces with kindness.
"…Alright. I’m not well-versed in sex. To fuck you as brutally as in that video, I’m not skilled enough yet. What should I do… Will you guide me?"
"…Look at my hands… ruin me there… overwrite my hands with yours…"
"…"
"If you want me, I’ll give you everything. So… give me all of you… With your hands, your lips, your cock… ruin all of me…"
"…You want me to dominate all of you?"
"Yes… just for now… I’ll entrust my heart and body to you. So… just for now…"
"—Won’t you be my ‘master’?"
…Ahh.
Hearing Lucifer’s plea, Alastor narrowed his eyes slowly.
He understood what Lucifer wanted from him.
…He was begging, "I can’t satisfy myself alone, so dominate me and serve me."
What a selfish, unreasonable man—making such an outrageous demand of a near-stranger like Alastor. It was proof of how much he’d let his guard down around him, but inwardly, Alastor was exasperated.
A roleplay of master and slave.
All of it was just consensual play, nothing more.
In the end, their future selves were likely just "acting" out these roles too.
A sinner and the King of Hell—Alastor and Lucifer were beings entirely different in power, ideology, species, everything.
But on the bed, they could taste and enjoy each other’s bodies as equals. That must be their future relationship.
And that was a sophisticated form of sexual communication, impossible without mutual trust.
Lucifer had just handed Alastor the reins of trust.
With an invisible collar around his neck, he gazed at Alastor with longing eyes.
Alastor gave him the words he desired, fulfilling his request.
"…Even if it’s because that video drove you mad, willingly degrading yourself to become the slave of a sinner like me… You really are a shameless slut."
"… ♡ Ah, ahh…"
And yet…
Despite being demanded such an absurd play, Alastor had no choice but to agree. He had to cling to it.
Because this—sex—was the only way he knew to dominate the man before him, the only means he had right now.