Dungeon Diver: Stealing A Monster's Power - Chapter 16

After Reincarnating into Naruto World at the Warring State Era as an Uzumaki, Masahiko thought that he got a useless System. He lived for 48 years as a normal, below average Uzumaki Shinobi.

That changed when he finally knew how the system works the day of his 49th Birthday!

- Description from Novelupdates

The Revered Master, Yu Yan, known as the number one in the cultivation world, waited for sixteen thousand years, and finally took in a disciple. He taught her carefully, and took care of her diligently. He watched her as she slowly grew stronger as she comprehended the laws, and just as she was about to soar into prominence… she died!

A hundred years ago, Chen Qingyuan entered a forbidden zone called Sky Abyss, where his soul lamp extinguished, and everyone believed he had died. Today, although Chen Qingyuan has emerged alive from the forbidden zone, his cultivation has been completely crippled, and his spiritual roots are shattered. Faced with the remorse of lost love and the oppression of various sects, how should Chen Qingyuan proceed?“Chen Qingyuan, I'll give you two choices: one, marry me; two...”Inside Sky Abyss, there lives a girl in a red dress, with eyes like stars and a gentle voice.“I choose the second option.”Before the girl in the red dress could finish speaking, Chen Qingyuan decisively made his choice.(Main character with a dark belly + no system + humor + traditional fantasy + weak synopsis)

As a promise, he went out into the world as an assassin. 3 years later, after becoming the Supreme Assassin, he gave up on everything he had and returned to the ranks of ordinary people. But one day, Kismet, a mystical game created by the National Research and Development had appeared.