MTL - 80’s Sweet Marriage: Struggle for a Good Life - Chapter 9 That schoolbag is so ugly

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.

It begins on the mountain.

With the glint of a knife, a flash of steel in the hands of a sworn brother. A betrayal.

Stabbed and pushed down the mountain, Zi Chen lied within the red-stained snow, left to die.

This is where it begins; he is given life by lightning,
baptized by thunder.

Those who had once betrayed him should all suffer in his cruel revenge.

- Description from Novelupdates

She was originally the young miss of the Marquis Estate, but became a peasant girl due to a mixed-up at birth.

“Impossible… Why are you not following my orders!? Clearly I sucked your blood, why!?”

On the very first day of high school, the youth subscribing to the philosophy of “absolutely ordinary everyday life,” Kujou Hisui, encountered disaster head on: He was attacked by Rushella Daamu Draculea, the vampire who had lost her memory. Rushella was greatly intrigued to find her vampire powers ineffective against Hisui. Not only did she make Hisui’s home her own, she even enrolled in his school to stick to him–

Hisui had no choice but to help Rushella regain her memory. But before one crisis could be resolved, many more had risen. With tempting advances from the mysterious Sudou Mei, and kidnapped by the girl from the Supernatural Investigations Section in search of Rushella, Hisui’s ordinary life has been replaced by its complete opposite, drama–

Romantic comedy and supernatural action in a school setting!