I wasn't expecting someone to arrive so soon.

He managed to find this place.

The middle-aged, overweight man asked, "How does it work?"

I replied, "It's surprisingly simple. You just need to lie down in the magic fountain. You'll be able to breathe underwater. I suspect it will probably feel weird, though."

"What do you mean by 'probably'?" he asked. "I actually don't need to breathe. I don't even have lungs. To be entirely honest, I'm not really sure how any of my physiology works. I do have blood that’s pumped by a beating heart, but it seems to just exist to maintain my body, not like human blood that carries nutrients. My blood is filled with magic, and it seems to circulate mana throughout my body, nourishing me. I don’t need to eat, but if I do, whatever I consume is converted into mana. So, I’m not sure if the sensation of breathing underwater would feel strange. It’s just an educated guess."

He nodded in agreement. "I recommend going in naked. The process may destroy your clothes, so unless you want to head home naked, you're better off entering the fountain without them."

"Once you're in the fountain, it'll take a few minutes for the process to start. It’s going to inject your body with mana to force an evolution. The potential outcomes are straightforward. You could become a Majin, which is a type of monster. Don't worry, you'll still be yourself even if you evolve into a Majin. In fact, there’s an upside—Majins are made of magic and have a stronger affinity for it than humans. They also have long lifespans and are easier to evolve further than humans. Another option is Sage, which is just an evolved human. Sages are stronger, live longer, and have abilities that manifest depending on your subconscious mind. Whether you become a Majin or a Sage depends on you well your subconscious.

"That said, you won't be able to use the fountain to evolve further. It allows only one evolution—whether from human to Sage or Majin. Future evolutions are a matter of the soul, not just the body, and they require personal effort. There’s no shortcut for that.

Although, to be fair, Earth doesn’t naturally support high atmospheric mana levels; they're too low. The fountain draws energy from the ley lines, which is only possible if you're situated on one. However, the world’s magical energy is limited, so while it can power the fountain, it wouldn’t support large numbers of people using magic. Most of the ley line energy is being used to maintain the magic shield that protects Earth, which is why mana levels are so low. Earth's mana levels typically resemble those of younger worlds—this should not be the case since worlds with life develop more quickly. But here, the mana isn’t present in the atmosphere in high enough quantities to support natural evolution.

This tale has been unlawfully lifted from Royal Road; report any instances of this story if found elsewhere.

The fountain is a tool that forces an evolution, but evolving further requires personal effort because it involves the soul, not just the body. Soul-related evolutions are difficult and consume a lot of mana, and Earth doesn’t have enough energy to sustain that. You’d need to find alternative methods—probably soul reaping, though I wouldn’t recommend it. Lady Death might take offense. Well, whatever. Don't mind me; I’m just rambling."

The man nodded, and I directed him to the fountain. "As I mentioned, your clothes might be destroyed, so I recommend removing them before entering. Just lie there for a few minutes, and the process will begin. If you pass out, you’ll die, and it’s going to hurt like hell, so do everything you can to stay conscious."

I left the room naturally. It’s soundproof. Fortunately, I added a function to the fountain that turns corpses to dust by draining all of the body's life force and returning it to the Earth, which helps replenish the world’s mana. Even though modern-day Earth doesn't have much mana, there’s still a certain amount in the atmosphere. Most of it can be extracted from ley lines, but you need to be directly above one. Sorcerers generally don’t draw power from Earth itself because it's too difficult and unreliable, depending instead on dimensional energy, which can be accessed from anywhere. I'm surprised Earth’s sorcerers don't tap into the World Tree. Anyone in the Nine Realms should be able to draw from it without worrying about dimensional interference. It seems like a no-brainer, but whatever—it doesn't matter.

Three hours later, I opened the door and found a young man, about twenty years old, with the body of an Olympic athlete.

The young man, who looked like he was in his 20s, definitely had the physique of an Olympic swimmer.

He had two horns.

"Oh, he's a kaijin. This is interesting. I suspected he would become a demonoid, since that's how it works in That Time I Got Reincarnated as a Slime. Though I suppose, maybe in the Marvel Universe, that would be considered a failure, since demons are just naturally inclined to evil. Yes, Marvel demons are kind of like that—unrepentant and evil for the sake of being evil. They're the cliché demons everyone imagines: beings born pure evil, who can never be good because they're inherently evil.

It's something I’ve always disliked about them. Although there are plenty of interpretations where demons are just a race, Marvel demons typically tend to be evil.

Though I could say that Sophie is still technically a devil lord, and she doesn’t seem to show any effects. But perhaps it doesn’t apply to her, since she came from another universe. Hell, there could be some unknown factors I’m unaware of. After all, I do believe another Majin, who was formerly human, evolved into a different type of Majin. So, it’s entirely possible that there could be multiple different potential evolutions for a Majin.

Though kaijin is a bit unexpected."

I told the young man, "You're a kaijin. It's an evolved form of an ogre. It's between the ogre and oni evolutions. It goes ogre, kaijin, then oni."