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

Not too far in the future, Alastor held up the DVD of their sex with a skeptical look, speaking to Lucifer, who lounged on the bed in a bathrobe.
"…Your ideas really do wreak havoc on everything around you. Sending a video of us having sex to our past selves as some kind of thrill spice… How blasphemous. Is that why you fell to Hell?"
"Hahaha. I’m in a good mood today, so I’ll let that lame joke slide once—but say it again, and I’ll break your fingers. …It’s fine. I sent it to a past with the potential to reach this future, so no time paradoxes will happen. The outcome stays the same; only the process shifts slightly. Isn’t it fun that we can meddle with the journey, even if the destination’s fixed? …Besides, this is like charity…"
"Hm? …You say interesting things. Sending this perverted video is supposed to save the past you?"
"I know myself best… Back then, after parting with my wife, I was miserable, stuck in a rut. Bored out of my mind, unable to die, I didn’t yet know the perfect master standing before me could save me. …I had to teach that pitiful me how amazing it feels to be your slave, to be fucked senseless. Living on ignorantly for so long would’ve been tragic. …See? Kind of me, right?"
"Heh, you jest. …You’re truly the worst, most dangerous villain. You knew from the start that if the past you saw the current you—my slave—he’d choose ruin out of envy. You’re imagining how that desire-driven past you slowly, surely breaks chasing me, and you’re enjoying it, aren’t you? Greedily devouring even your past self—I’m obsessed with your honest avarice."
"…Haha. You see right through me… Watching something I’ve touched and shaped change over time is… delightful. Especially if it’s my lover—you—or the pitiful me no one else would save."
"Oh? You cared about me too? That’s news to me."
"W-Well… yeah, I guess. Don’t make me say it, it’s embarrassing… I just wish our past selves would hurry up and fall this far. This world with just the two of us is so comfortable, thrilling, and hopelessly dear…"
Seeing Lucifer’s joyful expression, Alastor smiled gently.
The man before him looked so peaceful and happy—hardly the type to execute such a diabolical plan of steering their past selves toward ruin by showing them an unavoidable future.
Alastor adored this side of Lucifer—his cruel, incomprehensible nature that transcended human ethics and norms.
"You’re captivating when you talk like that… Can I kiss you?"
"A kiss won’t be enough… Al…"
"Yes… I know. You want a reward, don’t you?"
"Yeah, Al… I love you…"
Savoring the touch of their lips, Lucifer whispered sweetly to Alastor.
"If I… wished to entrust everything to you… would you catch all of me?"
What a wicked man.
He knew full well Alastor couldn’t possibly handle all of him, yet he asked anyway.
The beloved lover before him reveled in playing the slave… a femme fatale fallen angel who wouldn’t hesitate to ruin even his past self for his own pleasure.
A mere sinner like Alastor could never contain the boundless desires of a former seraph.
…Even so, he wanted him.
He wanted to make Lucifer his.
Ever since their first time together, Alastor had been utterly captivated by him.
So he’d keep giving him the answers he craved until he tired of them.
That was one of the few forms of love Alastor could offer.
"Of course. If you wish it, I’ll do anything. …So you—stay mine alone, alright?"
"Yes… that’s perfect. …Never let me grow bored…"