Counterattack System appeared when I'm already At The Mahayana Realm - Chapter 48 - : The Oldest Person in Jiuzhou

After breaking up with his girlfriend, he accidentally acquired a genius system and rose from there against the heavens, becoming invincible..

- Description from Novelupdates

Freshman student Yang Dingtian possesses the Nine Yang Body, found only 1 in million. His Yang Fire is incomparably vigorous and thus, he cannot be near a female’s charms for his entire life. On the night of his 19th birthday, he decided to bid farewell to his virgin life. After stealing and tasting the forbidden fruit, he spontaneously combusted as the result!

One day every human on the world suddenly receives a mail claiming to enact the World Salvation Project. Half in doubt Kurosaki Shion, a diligent university student and loner, follows the mail’s instructions, becoming one of a million Demon Kings governing his very own Domain in the new world.

*** This is a post-apocalyptic story containing many fantasy elements. It is a somewhat dark tale following Shion as he grows while aiming for the unification of the all too sudden new world. It has many game-elements bolstered by strategical thinking while at the same time providing funny moments and romantic encounters.

During the Yongle period of the Ming Dynasty.

Zhang Anshi was ignorant, and he committed a heinous crime.

His brother-in-law is the prince? Oh, that’s all right!

- Description from novelbuddy