Counterattack System appeared when I'm already At The Mahayana Realm - Chapter 652 - 651: If Cultivation Techniques can be Sold

In a modern world where cultivators need a place to cultivate or vent their boredom, there are private businesses that set up instance dungeons with the aid of technology and cultivation magic to enable cultivators to train and commoners to experience the life of cultivation. They are called dungeon suppliers.
Xie Jin's one and only dream was to be a dungeon supplier and when his only relative passed away, the relative's inheritance gave him a plot of land and surprisingly, a 'System' Module which the relative had previously used.
With the help of the system, Xie Jin decided to pursue his dream of becoming the number one dungeon supplier.

After successfully reaching the Core Formation Stage and forming his Golden Core, Bai Langtian was betrayed by his own Master. His core was ripped from his body, and he was thrown off a mountain cliff into a valley full of demonic beasts.Thankfully, he survived the fall, and met his senior sister, Shangguan Yue Ling.She too had been betrayed by the same Master and pushed into this valley ten years ago. Ever since, she had been surviving alone by eating the corrupted flesh of demonic beasts.Now, Yue Ling revealed to Langtian a new path of cultivation:Demonic Cultivation.To reclaim his strength and take revenge, he must consume the flesh and essence of ten thousand demonic beasts.

When disaster struck, Ling Mo knew that the kinds of zombies depicted in doomsday movies would in fact, be totally different from reality…

An otaku with a hobby of masturbating was reincarnated as the son of a great mage.

As soon as he was born in this life, he vowed with a goal of embracing women till his death.

That said, when he became 20 years old, the Demon Lord which was sealed by his ancestors revived, and now it is his role to seal it once again.

And that demon lord is sealed in a tower dungeon that is rumored to be impossible to capture.

However, by an unexpected coincidence, he had found out that the Demon Lord is also one of him, a kindred spirit from within,

so he joined her instead and filled several traps in the tower dungeon, and thus they enjoyed a s*x spree with all the women coming over!