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

As the ancient grade beast Xiang Liu rose from the ocean, an enraged Mark didn't give it any chance to even launch an attack and proceeded to unleash his most reliable skill, Thunderblast.

In just an instant, a scarlet-colored lightning bolt descended from the false sky and struck one of the snake heads of Xiang Liu.

The lightning bolt then tore through the snake's head and went on striking the neck before destroying its core and killing it with one move. No battle occurred here. It is just one-sided annihilation.

Very soon, as the corpse of the beast slowly drowned in the ocean and disappeared, a floating beast spark appeared in Mark's sight but he ignored it and walked through the portal after dismissing the clone.

The trial of the Holy Beasts (part-6)