Reincarnated as an Energy with a System - Chapter 1312 Feast

As a promise, he went out into the world as an assassin. 3 years later, after becoming the Supreme Assassin, he gave up on everything he had and returned to the ranks of ordinary people. But one day, Kismet, a mystical game created by the National Research and Development had appeared.

Enigmatic hands, spectral frame, and one cunning strike just like the swing of the Grim Reaper. The Supreme Assassin takes on the mystical world, and how his legendary tales sets off, progressively ascending the altar to becoming the best.

- Description from Novelupdates

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.

In her previous life, her family was destroyed.In this life, she was reborn and decided to save her family, never letting history repeat itself. But with all the men in her family having already sacrificed, how can her family rise again? At this moment, he appeared and said, “Your family belongs to a prosperous lineage, and for a hundred years, there has never been any waste of talent, including among women.”Later on...The eldest sister became an invincible warrior, the second sister a formidable head of the household, and the third sister a wealthy merchant. Her family was rejuvenated.Because he had helped her countless times in her previous life, she secretly returned the favor in this one.On a snowy night, outside the city wall:“You've saved me so many times, do you like me?” he asked.“No, you are mistaken,” she replied.“Then if I've saved you so many times, can you grow to like me?” he asked again.

Living things really are ignorant – the greed to obtain the key to knowledge and the fundamentals of energy overpowers them. Little do they know that knowledge is full of lies and energy is the root of destruction. Us, mages, have mastered travelling through space and time. We are invincible, we can turn worlds into dust and you, mere ants, will be wiped out with no trace.

-Mage Adam

An A.I.(Artificial Intelligence) gets reincarnated into a world where he becomes a mage.