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

He took out the scarlet feather of some bird from his storage ring and handed it to the second prince, "this has been passed down in our family for generations and so far, it was used two times in history. When you feel like you need help, pour your ether energy into this feather. The Phoenix will hear you and come to the rescue. However, it can only be used for one more time.

Perhaps, the war could be won if I used it but deep down, I probably know that Western Yan isn't ours to begin with. It is an occupied territory. I guess I wasn't desperate enough to use this last remaining treasure of the Shang Dynasty after losing both of our divine-grade weapons.

Today, I will give you this so that it becomes your life-saving treasure."

"But, Your Majesty, shouldn't this be handed to your successor?" Shang Wen was quite surprised when he heard the history behind this feather which looked quite normal at one glance.

Emperor Shang announces his retirement