Kyoukai Senjou no Horizon - Volume 1, Chapter 01: Participants in a Chance Meeting by the Storefront

A lowly child beggar, a noble prince, a monster viewed as the enemy of the entire world. If you possess all three identities at the same time, which identity would you choose to help you earn a better ending?

After Wang Mang died, he turned into a giant python and evolved like crazy!

With the help of his family, he grew bigger and bigger! From the first few meters to tens of meters, and then to hundreds of meters!

From Burmese Python to Titan Python, and then to Deep Sea Python! When Wang Mang’s size reached hundreds of meters, the earth took a sudden change and the disaster came…

He Lang died by his own hands for the sake of his imperial younger brother’s ambition, whom he loved. He was offered to be reborn in exchange for giving up his past romantic feelings. Reborn without the burden of his romantic feelings, he brings with him a manual to new worlds. He wholeheartedly followed the instructions of the manual to complete the tasks, not knowing that the originally slag gong was blackening…
He pleaded to his affectionate Emperor brother to release him, he pleaded to the paranoid prisoner next door, but until the end he remained baffled.
In the end, he discovered that the full name of the manual was – “Slag Shou Cultivating Manual”
Σ (っ ° ° °;) っ!

- Description from Novelupdates

In a distant future, the empires of mankind span the galaxy, and glorious Earth has devolved into a peripheral backwater.

In Shanjing city in the Asian region, Wang Zheng’s dreams of becoming a mech pilot are crushed when his college entrance exam genetic score turns out a pathetic twenty eight, barely above an animal.

To make things worse, people get the impression he attempted suicide after being rejected by the campus beauty.

Then the closest thing to a family he has, the old man in the book store across the road, goes missing, leaving him only a mysterious birthday present.