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

Ruins of Khambhat, Eastern Sun Kingdom;

Located on an island, just about 10 km away from the coast of the mainland, the city of Khambhat held the throne for several centuries.

However, from the late 12th century, the kings stopped living in the forts and shifted toward castles and palaces.

Using an excuse that a king should live with his people, not far away, one of the kings shifted his base to Helios City and used the Fort of Khambhat as a citadel to protect the civilian officials and the treasury during times of war.

As if the god decided that the king made the decision right, over the next couple of centuries, earthquakes disturbed the ocean, and frequent low-magnitude tsunamis caused a lot of damage to the island city alongside the other islands nearby.

From Khambhat to Earth-486: Unexpected Journeys