After returning from that world, I noticed that barely any time had passed here, even though I had spent nearly a month in 10,000 BC. I only realized this now—last time, I was too excited and didn't stay long enough to notice.
But now it's clear: a whole month there translated to only about five hours here.
During that month, I spent my days hunting, eating, and enjoying a quiet life away from the modern world.
Surprisingly, I didn't miss modern conveniences much, since I had good food and entertainment thanks to Athena—it literally downloaded every movie and anime into itself, so I never got bored.
It felt like a vacation. On top of that, I earned plot force simply by staying in that world. With the rate being 10 P.F. per day, I collected 300 P.F. from my stay.
Combined with all the hunting I did, which rewarded me another 3,900 P.F., I ended up with a total of 4,200 P.F. After converting, that came out to 420 U.P.F. (Universal Plot Force). I still don't know if that amount is considered much or little.
I had so much fun in that world. I deliberately held back and relied only on my body, never calling on Raphael, Beelzebub, or Sticky Thread in combat.
Using them against prehistoric beasts would've been massive overkill—like swatting a mosquito with a Star Destroyer. Instead, I fought with my bare fists, something I had never truly done before, and it turned out to be exhilarating.
The thrill of close combat was addictive. I guess this means I'm going to be a combat mage after all.
Even after all the time I spent in 10,000 B.C., I only managed to climb from 8-A to 7-A—though that still means I can now destroy a mountain with ease.
Now that I understand my limits and what I still need, the real problem begins: deciding which world to visit next.
There are so many I want to explore that I couldn't make up my mind. In the end, I left it to chance—I fed all my personal choices into a random generator and let fate decide.
The result was unexpected. It wasn't a movie world, but the Demon Slayer anime world. I asked Athena how much plot force was required to visit, and it was just 20 U.P.F., so I decided to go.
With my mutated Beelzebub skill, I already possessed the ability to read the memories of any defeated or subdued enemy.
This made my plan simple: by accessing Muzan's memories, I could extract the precise procedure for creating the Ghost Serum. Since I already knew where to find the Blue Lily, synthesizing the serum would be effortless.
In other words, I could recreate the perfect Ghost Serum with complete certainty—turning Muzan's own knowledge into my power, without worrying about trial and error.
I then entered the world of demon slayer, remaining untraceable, intangible, and invisible.