This is a sci-fi world nearly identical to the modern day.

One major difference is the discovery of a certain factor.

——That factor is known as the "Soul Factor."

Proposed in 1836 by the philosopher Samuel Cohen, the Soul Factor was officially discovered in 1879.

Samuel Cohen had already passed away at the time of discovery. After his death, public perception of him shifted from a dubious charlatan to a great prophet.

There is one important detail.

The Soul Factor does not allow the bearer to see their own soul; it is limited to blood relatives or those with a close psychological bond to the bearer.

In other words, the inner workings of the Soul Factor are a singular phenomenon that only specific individuals can observe.

Let's return to the modern 21st century. This is a young boy's diary.

—Current Timeline: 8-year-old Iori Arc—

(It's tucked deep inside his desk, likely because he absolutely doesn't want it found. He probably thought his friends would crack a phone password in seconds.)

"DIARY! NO PEEKING!! 1 MILLION YEN FINE IF YOU LOOK!!!"

Month ○, Day △, Thursday, Sunny, Iori Nemoto

I don't really get it, but they found something called a Soul Factor in me during my checkup.

Apparently, I have to go to some complicated-sounding place in Tokyo called the Soul Factor Observation Center.

Guest is coming with me!

I'm gonna tell them I want to go to the Tokyo Water Center!

Whoa! I'm actually getting excited!!

—Past Timeline: Iori's Past Life, Leonard Arc—

Leonard, the person connected to Iori via the Soul Factor. The memoir of a Western knight that might be sleeping in a storehouse somewhere.

"To my beloved,"

I must confess. Were you truly the one I was searching for?

To be honest, I do not know. ...It was exhausting trying to find you among so many marriage candidates. You were not at the meeting at first.

Long ago, when I lay fallen on that battlefield, you—a stranger—used a strange-smelling liquid and a clean handkerchief on me.

Because of that treatment, I am able to write this letter and think these thoughts today.

...My beloved. If I ever truly feel I have found you again. I will not let you (⚫︎).

(Part of the text is blurred by what looks like tear stains and is unreadable.)

—Future Timeline: 18-year-old Iori Arc—

Guest met the past-life Iori, Leonard, as a 24-year-old through the Soul Factor. While returning to the present, time crossed wires, and Guest jumped 10 years into the future for 5 minutes.

There, Guest saw the 18-year-old Iori Nemoto, grown up from his 8-year-old self. In that future, he trapped the modern-day Guest—who was in the body of their 10-years-older self—in his arms.

"Hey, Guest... I... I met you much earlier than this. If things stay like this, I'll..."

Guest returned to the present from that scene.

With past-life memories returned, can Guest avoid the yandere future of the Iori 10 years from now?!

A modern bratty shota's yandere turn in 10 years is unavoidable? No way!! 💥