Maybe a Fake Gintama - Chapter 5: [Monster] and [Little Monster] and [Son of Monster]

In the Canglan Continent, there existed a rule: only those who managed to awaken a Martial Spirit were able to pursue the path of cultivation, and a Martial Spirit’s rank was determined when it was awakened. Born in Linshui City, Qin Nan was a peerless genius who possessed great talents and was highly anticipated to become a great cultivator in the future. However, things changed when he ended up awakening the lowest-grade Martial Spirit, resulting in him being considered trash.

As he woke up, Wei Xuan realized he returned to the day when the apocalypse had just begun. Wei Xuan, who had a second chance at life, immediately decided: not to go to a survivor base, and not to return to human society, instead, there is only one thing he wants to do now. Find the half-zombie Du Hang, and live with him in the city full of zombies, farming and living together until old age. Wei Xuan, who stayed in the zombie city after being reborn, unexpectedly found out that zombies are not as terrible as humans think…

- Description from Novelupdates

By the time I reached thirty, I hadn't managed to provide any of the happiness I wanted for my wife.I also still couldn't become the support my parents relied on.At this turning point in my fate, my income suddenly began to increase randomly.(A daily life tale in a wealthy family setting, featuring a single female lead and no harem.)

The MC entered the body of the An family eldest son, An Ziran, an arrogant 16 years old boy who weighed 78 kg (~171-172 lbs), who only knew how to eat, play and sleep. Seeing his current body, An Ziran decided his first priority was to LOSE WEIGHT!