Bog Standard Isekai - Chapter 51Book 4.

Our straight (?) bottom woke up ten years into the future and found himself on the bed of his childhood friend… At the start, the bottom was shocked to his very bones, but he soon quickly accepted this premise and found the whole situation to be rather amusing. Precisely then, the bottom once again went back to his timeline — back to when he and the top were just platonic childhood friends.

When he woke up, Zhou Sui became a low-level Qi refiner in the world of immortality. Fortunately, he obtained the most precious Gu god bowl, which can refine various Gu insects.

Refining the Spring and Autumn Gu can prolong life and make you immortal.

The refining golden cicada Gu can give birth to dead people, flesh and white bones.

Refining the Dragon Elephant Gu to gain the power of the Dragon Elephant, the body of the Dragon Elephant, and the indestructibility of the King Kong

But the Gu he refined for the first time was the Infatuation Gu.

From then on, he discovered a bright road to cultivation.

The years change, the mountains and rivers change, but I am the eternal Zhou family.

- Description from novelbuddy

Mark is a genius military weapon designer who was kidnapped by a mafia gang after refusing to work for them.
They forced him to design unique weapons for five years, until one day he successfully escaped only to get shot by his trusted comrades.
*Ding! You awakened a weapon system.
When he opened his eyes, he was in a different body and in a different world.
"You want to kill a wild boar without being detected? Forget about bow and arrow. Here, I present you this sniper rifle."
"You want to kill a horde of goblins from the sky? Forget about those flying carpets and brooms. Here, I present you the fighter jet."
"You want to kill a dragon? Forget about taking the help of the S-class adventure team. Here, I present you a nuclear bomb."
Join Mark Spencer/ Lu Zhen as he brings the whole world to its knees with the help of his weapon system.
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Note: Author isn't born in an English-speaking nation and has no editor either. So, please be understanding if there are any grammatical errors.
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Four years after the Third Nightmare, something unexpected happens. A group of people find themselves in a strange theatre, which tells them to react to someone's story...?