Snowstar

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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Author's current works: War Online, My Soul card is a Reaper
Author's other notable works:  The Last Slytherin, The Sharingan Hyuga
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You can also support the Author through Patreon

https://www.patreon.com/snowstar

Weapon seller in the world of magic

Everyone got up in shock. "Who are you?" Shang Jun roared in anger.

Steve neither gave his introduction nor did he bother to reply. He rushed forward at a speed that couldn't be captured by anyone in the room and swung his sword at the young emperor.

Before he knew what happened, Shang Jun's left hand rolled on the floor and he screamed in pain with his knees touching the floor while the blood started dripping at a crazy rate.

Picking up the hand, Steve said, "The true heir to the throne says hello."

"Who is there… Kill him…" Shang Jun shouted but no imperial guard responded. As he desperately looked at Cao Wen, he saw the monk was shaking in fear.

Steve then left the palace in a hurry, bringing the hand to the spider-ship, where Mark was waiting for him.

Mark directly placed the hand with a fresh wound in his inventory and patted Steve's shoulder, "Good job."

Launching the Space station