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

Description: This unnamed box was forged by melting down a number of Voidstones, a unique material that only grows in the Banished realm or the Void realm at the pace of 1 millimeter every 834,996 years. Due to their nullification properties, the box is nearly indestructible against the attack of any force under 15-circle (Elder God realm).

Weakness: The box is weak against forces such as Protos energy, anti-matter, Natural energy, pure divine energy, and Chaos energy.

Contents: It contains one of two keys to the Heavenly Palace's treasury. In the battle against the Chaos Lord, the Jade emperor lost his key to the cosmos, drifting in space for hundreds of millions of years.

Effect: The Box is immune to attacks and also weighs roughly 1.32 billion kg on the current planet.

*Ding! You triggered an emergency quest.

The Grand Auction (final)