When I Tried Strengthening a Rusty Sword, It Turned into an OP Magic Sword(2021)

[Sabitsuita Ken] wo Tameshi ni Kyoukashite Mitara, Tondemonai Maken ni Bakemashita

When everyone turns 12 years old, they are granted a Mystic Arms by God. The hero-admiring Rust dreams that he'll get a powerful one of his own one day.

As his fellow villagers began receiving high rank Mystic Arms one after another, Rust nervously prayed to God. Then, before him appeared a Mystic Arms of the lowest rank, a Rusty Sword.

A tale of becoming "zeros to heroes" with the weakest boy and the lowliest weapon!

(Source: Manga UP!)