Gu Si actually didn't know much about Gu Mang.
When they were young, people compared Gu Yin with Gu Mang.
They even advised Gu Zhen and Bai Xu not to waste money to find a school for Gu Mang, and to train Gu Yin with the money.
At that time, Gu Si was very angry and scolded the man with the rotten mouth.
Since then, Gu Si's reputation had declined. Just like Gu Mang, he became a bad role model for everyone in their county and at school.
Despite this, Gu Si would still lash out at whoever dared to insult Gu Mang.
Later, Gu Mang gave him a "Cultivation Guide", but it could not save him. He said the same sentence every time.
"You can insult me, but not my sister."
Gu Si only found out about some of Gu Mang's identity when she taught him how to use the computer. That was when he realized that Gu Mang had been pretending all the time.
But Gu Si felt that those were not all.