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

Mark neither had the strength nor the will to sacrifice his beloved attack helicopter. Previously, he had given up the Battle Tank for the divine sword. But, it was worth it. However, was the life of this king worth it?

Maybe, it's best to throw away the life of this old man. Having a submarine or a destroyer is good but they aren't worth compared to the attack helicopter.

As Mark thought of it as an impossible quest and had second thoughts about completing it, the system lured him into debt.

*Ding! The host can use the stone first and pay up later.

*Ding! 1 credit = 5 gold coins. The purification stone will cost 50,000 credits. 250,000 gold coins will be added to the debt.

Now the system is even offering a credit card?