I updated the 2nd version of the PDF eBook on a 6 x 9 inches (common paperback) layout. If you're interested in the old SEGA fanfiction in a short reading (ca. 4,000 words), check it out.
"The Underground"
https://pdp.xrea.jp/contents/The_underground_Azel_pdf_ver2.pdf
I made this story readable whether you know the old PD video game series or not. It's a short memoir by a middle-aged man living in a big and authoritarian empire.
The boy felt uncomfortable with daily life and Imperial managerialism.
The ancient ruins under the capital used to be his refuge.
One day, he got lost in the tunnel. A young explorer helped him,
and this mysterious companion led him deep into the labyrinth instead of the exit...
You can also read the story there if you have accounts on these platforms.
Wattpad:
https://www.wattpad.com/user/takujiyamamoto
RoyalRoads:
https://www.royalroad.com/fiction/65483/the-underground