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

"Sorry, I’d like to wet it a little… mind if I lick it?"
Lucifer spoke apologetically as he addressed the tentacle Alastor extended. His trembling lips brushed against the black, wriggling, octopus-like appendage.
"Mm… chu, nfu… haa, lero… chupa, ah… ha… n…"
He was likely treating Alastor’s tentacle as a makeshift penis, licking it as such. Though the goal was merely to moisten it with saliva, rendering the act somewhat meaningless, Lucifer’s hand caressed the tentacle tenderly, moving as if stroking a real member, his red tongue sliding alongside it.
"…"
The tentacle wasn’t entirely devoid of sensation, so the rhythmic stimulation—something Alastor wasn’t accustomed to—felt faintly ticklish.
"…Come to think of it… you were licking so eagerly in that video too. Do you enjoy servicing with your hands and mouth?"
"Haa… haa… s-stop it… don’t say such… cruel things… chu… lero…"
Even when humiliated with words, he didn’t stop. His aroused body must have been too unbearable to ignore. Alastor couldn’t comprehend humans drowning in lust, but he found himself intrigued by how Lucifer—presumably a man of great pride—continued to chase fleeting pleasure despite being insulted by him.
When Alastor shifted his gaze to Lucifer, he noticed that at some point, the man had lowered his trousers, exposing his lower abdomen. Lucifer’s member was fully erect. Even without touching it, just licking and fondling the tentacle had brought it to a straining, near-bursting state.
"Haa, ah… n…"
Lucifer slid his fingers along his own buttocks, beginning to tease himself inside. Each movement of his knuckles drew a restrained moan.
Alastor had heard the vulgar, saccharine moans from the video—moans Lucifer himself claimed were unmistakably his own—so he understood.
Lucifer was holding back. Suppressing the honest reactions of drowning in that intense pleasure. Was it out of consideration for Alastor’s presence?
…After watching that video together, it seemed a bit late for modesty. Was he trying to say that his current self was somehow better than the depraved figure in the footage?
Don’t play coy.
The moment you begged me—a man you despised—to "lend you my body," you became the same as that figure.
A surge of anger welled up, and Alastor could no longer stand idly by. He imagined his future self smirking, thinking, "So you’re finally stepping in." The idea of being used as a convenient tool for Lucifer’s pleasure was something Alastor absolutely couldn’t tolerate.
From behind Lucifer, who was indulging in self-p,easure with the tentacle, Alastor gently placed his hand over Lucifer’s.
"?!?!"
"…Getting all worked up while ignoring me. Does it feel that good?"
"Ah, ah… w-why…"
"I got curious—wanted to see if you’d make the same sounds as in the video. Let me help you."
Alastor pulled Lucifer’s fingers out and thrust his tentacle into the man’s buttocks instead.
"Nn!! Nn… nfu…"
"Don’t cover your mouth. If you do, I won’t lend you my tentacle."
"Hii… o-okay… don’t… stop…"
Alastor’s back trembled.
Was this what it meant to dominate a powerful being? With his own hands? This man before him?
A strange heat bloomed in his lower abdomen.
…Was he getting aroused? By the act of ravaging this man?
"Ah, ahaa… ♡"
A sweet moan slipped out.
The sounds from the video had been far filthier.
It wasn’t enough yet, was it?
"…Ha! ♡"
Lucifer’s lips let out a saccharine sound, and Alastor’s hips tingled in response.
…It was the same.
The man in the video and the one before him—were they truly the same?
It was all because of that footage.
Knowing it was undeniably Lucifer himself made it impossible not to overlap the figure in the video with the man in front of him. Realizing that "their relationship would eventually lead there" twisted his perception.
If this man would one day become that figure under Alastor’s hands—not in some distant future, but right here, right now—then Alastor wanted to claim him as his own.
The dark desire lurking deep within Alastor could no longer be restrained.
As a being born into the body of a "man" and having lived as one, Alastor had wielded that identity without hesitation.
Violence.
Fear.
All to dominate others.
He knew it well.
Even if he felt discomfort and aversion toward sex, even if he played the role of a rational clown who deliberately unsettled others or acted as an unfeeling conqueror trampling over them, he couldn’t escape the sweet pleasure of violence and domination.
Because he understood that it was the most exquisite thrill.