One Piece: Fist of the World - Chapter 12: Experiments with Devil Fruits

The night is dark and the wind is high, and the reality is killed.

Dear players, welcome to the holographic killing game “Fantasy”.

This game is not easy, don’t flirt with girls, don’t make friends, focus on hurting each other.

【Book Friends Group: 471036516】

- Description from novelbuddy

Nyx, Earth's former number one mercenary found himself on the end of his life failing to escape from a powerful criminal mastermind. However, fate seems to have another plan for him when he woke up in a completely different place, a place that he will eventually call home in the new world where strength makes one the biggest boss.[Welcome to the Universal Shop System!][Detected that it is the first-time log-in. Reward: Random Gift Pack (5)][Detected the user entering the Body Tempering Realm. Reward: Infinite Qi System][Opened Random Gift Pack (5). Acquired True Transcendence Body Art (1). Acquired Primordial Nihility Transcendent Qi (1). Acquired Immortal Illusion Art (1). Acquired Grand Desolation Transcendent Body (1). Acquired Extreme Origin Transcendent Soul (1)]With an absurd system as his cheat, follow the young man's journey through the entirety as he gains his position as the one true peerless existence, the sole transcendent above all.

500 years ago, Chen Xi was devoured by a crack in the void and was transported into a cultivation world.

500 years later, he returned back to Earth after enduring through several hardships and discovered that only 5 years had gone by.

…

In the courtyard, beauty at the side, a candle flame wavering.

A gush of clear wind, half a full moon, the peach tree remains unchanging.

…

Wait, whose kid is this?! Why is she calling me papa? Gazing at the little girl in front of him with skin as pale as jade, Chen Xi froze.

…

　
Returning home from cultivation, starting as a stay-at-home dad.

In this life, not fighting to be a king nor claiming to be a tyrant, only praying to peacefully be a wife-pampering mad devil and a child-protecting daddy!

- Description from Novelupdates

This is a story about the protagonist getting the system, going crazy in the biochemical apocalypse, producing aircraft and tanks, destroying zombies, saving good people and killing bad people.

- Description from novelbuddy