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 or buy coffee on Ko-fi.com

https://www.patreon.com/snowstar

https://ko-fi.com/snowstar5061

Weapon seller in the world of magic

"Guys, don't relax. The demon is a demigod. You can't underestimate it. And demon horde could attack us any time."

Mephisto gazed at one of the sect leaders and grinned, "Never expected one of the demon contractors would make a move against me."

"Sect Master Nie?" The other two couldn't help but glance at their ally.

Nie Zhouyang, with a grim face, said, stretching his arms, "The demon will spout any nonsense to escape. Don't waste time and kill it before it summons the demon horde."

The other two nodded and stretched their arms, too, pouring ether energy into their respective artifacts, which responded by gathering huge amounts of natural energy to form a concentrated beam of energy and struck the demon general at the same time.

A mysterious savior with name, "Allen?"