Terrible news! My deskmate's first chapter is gone!

No time travel, no system, no rebirth.
No slaps in the face, no gimmicks, no stupidity.
There is a strange sight in this world: the Black Tower.
No matter where you look out from on Earth, as long as there is an open view, you will definitely be able to see its shape.
And its distance from you is constant, whether you move forward or backward, and no matter where you are, the distance between you and it will never change.
My name is Chen Xi, and I am a patient suffering from hyperthymesia.
I remember every single thing that happened after I turned four.
One ordinary afternoon, my deskmate Lin Fan disappeared.
The whole world has forgotten him, except me...
(The introduction is insufficient; please read the main text.)