I Upgrade Everything in the Apocalypse

A post-apocalyptic world of martial artists.

A gaming shut-in transmigrates into the apocalypse as the useless young master of a wealthy family and awakens an upgrade System.

From the start, he upgrades his sniper rifle and body, and awakens skills.

Later, he upgrades the System, which grows stronger with every upgrade.

The stronger his body, the stronger the protagonist, in an endless cycle.