Immortality begins with Becoming an Alchemy Grandmaster - Chapter 986 - 399 Vicious Secret Technique Forerunner to

The world was once at war with 10 alternate worlds. This was known as the Concept War and our world won 60 years ago. All of this was concealed so no normal people are aware of this fact in the current time.

After the death of his grandfather, the high-school student Sayama Mikoto is suddenly summoned by the giant corporation IAI. He learns this world is headed for destruction due to the acceleration of the Minus Concepts. To prevent this, negotiations must be undertaken with the survivors of the other parallel worlds so their 10 concepts can be released.

And so Sayama is caught up in the final battle to clean up after the Concept War which left behind so much enmity.

Attribute Classification: Overhead/Western Magic/Strong Attack/Sweet

- Description from novelbuddy

There are all sorts of lunatics in the world:Self-centered, reckless, psychotic, impulsive, obsessive, and pe*verted.As far as Suin knows, that man embodied every single one of those traits—an obsessive, pe*verted psycho.And now, that lunatic is back.“Finally, we meet.”“Adult Lee Suin.”He didn’t even try to hide the sticky hunger in his gaze, like a starved lion finally spotting its prey.“A job reassignment?”“I want Lee Suin to help me.”Chairman Woo Ilhwa, unaware of his son’s true intentions, reassigns Suin, his chief secretary, to serve as his son’s personal secretary.This forces Suin into close proximity with the man who’s been preying on her from the shadows.“Wait for me, Lee Suin.”During his eleven years of exile, Jaehee had dreamed of one thing:A proper relationship—not as a restricted minor, but as a full-grown adult.A relationship where he could take what he wanted, whenever and however he pleased.That’s why, even though Suin was as rigid as a steel rod, his sly persistence ignited the spark within him whenever he faced her.“What do you want from me?”“You.”“Lee Suin.”But it seems Suin has been flirting with some bastard behind his back, and Jaehee’s jealousy and obsession explode.“Don’t take a single step.”“Unless you want to see me go completely insane.”What nonsense.You were already insane to begin with.

When she woke up, Lake returned to the classroom of the third year. The classmates were in class with swords and sticks, and the teacher became a female Taoist.
The little fat man in the back seat, how to put two big hammers under his chair.
Rick found this to be a global era!

- Description from Uukanshu (translated)