MTL - Holistic Fantasy - ~ 010 One person? Estimate the error?

A college student was returning home after studying abroad for several years when the end of the world happened. A dragon appeared out of nowhere and attacked the plane he was in, thanks to an incredible amount of luck and his quick-thinking, he managed to survive the plane crash only to get stuck on a tropical island. A weird system took over the world and brought monsters to Earth. While nations collapsed and the world as a whole was being destroyed by ridiculous monsters, Leon was stuck on a godforsaken island with no chances of being rescued. What will happen to him? How will the world change while he is away? Will he even manage to return? The story, all names, characters, and incidents portrayed in this production are fictitious. No identification with actual persons (living or deceased), places, buildings, and products is intended or should be inferred.

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.

The world was destroyed, torn to shreds by the war as it raged on. With the falling of nuclear bombs, the mutation strangely adapted and became an entirely new element.Those who couldn't withstand this mutation became beings tethering on the edge of life and death, becoming undead.Only a small population remains on the earth now.In this small population, some can adapt to the mutation and awaken unique powers in the apocalypse, while others are entirely unaffected, still like normal people.Ray was just a normal E-class awakener, but a faithful purple crystal changed everything.Through the purple crystal, a “system” activated inside him, which could allow him to get stronger the more he spreads his genes.Necromancer, wizard, martial artist to sorcerer - every single skill was possible as long as he spread his genes.From that moment, Ray walked the path of spreading his genes “for the sake of humanity.”#no ntr, yaoi or yuri

What’s not to love about my new life after transmigrating into a Pet-centered world?
There are mighty creatures that come in all shapes and sizes. They can either be cuddly companions, helpers in your daily life, daring scouts or strong fighters. Or all of the above. Not bad, huh?

I have a family, but the fact is completely overshadowed by my younger sister. She thoroughly hates my guts, and she makes sure that I know this. Every. Single. Day.
Did I mention that she’s disgustingly talented while I am a bottom feeder? A terribly handsome one at that.

I have free rein to run the family business on my own. A small and quaint Pet Store. It should have been great if not for the fact that the previous owner of this body was born with ZERO affinity to handle Astral Pets…

It wouldn’t be a proper transmigration without a gimmick or a system to pave my road to greatness, don’t you think? I have one, but I don’t know if I would be better off without it…