Three Days of Happiness - Chapter 1 A Promise For Ten Years Time

After dying in an oddly anticlimactic vending machine accident, Kazuki Ren is reincarnated in the demon realm—not as a hero, not as a villain, but as the only human male student enrolled at the mysterious Academy of Ruin, a school where all the professors are demon lords and all the students are powerful, beautiful she-demons.Ren is told he has one task: survive.But there’s a catch. The Academy’s darkest secret is about to awaken, and Ren holds a hidden power that could either destroy the demon world... or rule it.Now surrounded by seductive demons with hidden motives, eldritch tomes, forbidden dungeons, and twisted exams, Ren must master his ability—or be consumed.Magic, mystery, danger, and temptation await in this dark academia harem fantasy.

“After every fire, ants survive.”

…

Mysterious anomalous biological metals have polluted the world, and the world has undergone tremendous changes. Metal sickness is like a key that opens the door to evolution. Under the tide of evolution, there are no innocents.

The choice is up to you, do you want to be the surviving ants after the fire, or do you want to risk your life, step on the glorious long steps to the gods, and glimpse the supreme glory of the mother goddess?

…

Touch the totem in your heart, follow the inspiration, and step on the long steps of ascending to God:

[Amphibians] → [Atlantic Glory] → [Ningen]…

[Eight Arms] → [Nightmare in the Sea] → [Deep Divers]…

[Eagle Eye] → [Owl Ghost of the Night] → [Jersey Demon]…

[Living Dead] → [Grave Digger] → [Death Ferryman]…

…

“On that day, the world was polluted, and I was the source of pollution. Human desires are endless, desire is the best food on the way to evolution, and I am the embodiment of desire.”

– Joe Tour.

- Description from novelbuddy

Xiao Yu, who was a student from modern Earth, accidentally transports to another world and becomes the lord of a territory. Facing an unfavorable situation, he vows to take back his family business, build his new territory, kill all of those who covet his wealth, and dominate the world!

In the era of steam and mystery, becoming a correspondence student at the Thaumatology Academy was something Shad never thought of.

A whispering voice rang in my ears, who was reciting the poems of foreigners——

The old gods and aliens,

When the brassy rings of fate turn,

The golden runes are flickering.

steam surge,

the fire flickers,

Relic echoes,

The old gods revived.

The outstretched hand after the thick fog,

Pull back the hazy curtain of the crazy age.

Guests from afar explore the lands of the Old Continent,

Striking the melody of the next era.

Came here through the gate of time,

Shad put down his suitcase,

Look at the silvery moonlight overhead.

- Description from novelbuddy