My Genius Sister is Only Seven!? - Chapter 217 - Confession From Downstairs

There are a total of seven sins, and a revelation is made to a young man named Alex that he is destined to become a demon lord, more especially a demon lord of sin called LUST.

It's not like he can change that and because he always knew something about himself was different—not in a physical sense, well, maybe a little—and not in a mental sense—but rather because he is thrown into a demonic war that compels him to accept his new reality.

He was only aware of a difference in himself. Relating to him and the ladies who are drawn to him... Well, it was more or less like he was a magnet in front of all the girls, and all the girls were drawn to him like a metal.

A Federation Colonel with abnormal thoughts was locked in a dark room and met a little looney.

“Your whole body emits a scent that I dread (covet) and fear (desire).”

A frigid Colonel X little looney roommate: A sweet story of interstellar travel

- Description from Novelupdates

She is a top-class spy, a poison specialist, but also a young and cute girl with a sinister temperament. In spite of her sweet and innocent appearance, she can complete any tasks without the slightest hesitation. One day because of an incomplete black magic, she was sent into the body of a girl who was deemed as a good-for-nothing. What kind of change will she bring to this continent?

Rakna was not normal. No, unmistakably not.

Whether it was his appearance, his personality, his abilities, his identity, nothing about him had ever been banal. Was it his choice?

No. He was merely but a tormented soul doing its utmost to live the life it had learned to never enjoy.

Would being picked by a glorified universal abductor calling itself a system bring something out of him?

Would he finally learn to breathe in the pool of blood that suffocated him? The Harvester does not sow, he only collects.

All he has ever known to feel was loss and the only thing he can do is take.

He will devour their hearts and drink their blood if it is what it takes.