Marvel: Rise of the Ultimate AI - Chapter 70: The Fall of Doctor Octopus

Sometime after ‘Gates’ appeared in this world, humanity was divided into two: [User] and [ordinary human beings] Lee-kyung was able to awaken into a user and choose a [Class]…but, in momentary misjudgement, chose to be a [Necromancer], the worst of all classes.

Lee-kyung, searching for the materials to evolve his skeletal servant, ‘Lackey,’ was barely able to participate in a high-level raid for [Tower of Command] Dungeon. In an accident, he falls down alone to uncover a hidden conspiracy.

Injured and desperate to survive, Lee-kyung called out to anyone…and reached a vengeful spirit. “Please, I’ll do anything….Please form a contract with me and save me!”

–-You’ll do anything?….

TW: Depictions of mental health

Offered as a bride to Hades at the age of eighteen.

Pestered by evil spirits in the day, and taken advantage of by a perverted demon at night.

Pervert: “Dear, a night with you is worth more than gold.”

I leaned away as I clenched my teeth angrily: “Worth my foot!”

- Description from Novelupdates

Some say reincarnation is a blessing, but for me, it's a dreadful curse. Cursed with endless reincarnation, I've been reborn as a villain 137 times. And all 137 times, I've been toyed with and killed by heroes who are far more cruel than the said villains... If I can't win no matter what I do, then I'll crush those so-called heroes at their very roots. - Quality Fan Translations, Made by Fans for the Fans - Villain Takes Over The Academy

A girl who calls herself a demon appeared before a timid student named Fumio Kijima. The girl claims to be a campaign girl from the demon world and she gives him the ability to “summon a room” from nothing but thin air.

At first he doesn’t abuse his power and uses it as a convenient ability in his every day life. But one day he is bullied by his classmates under a false pretext and is made to suffer. In the past he would have wallowed in misery and cried himself to sleep, but now he had a power to call upon.

“I will make them regret it!”

Using his powers to summon his “room”, he begins his era of confinement and brainwashing to achieve his goals.