According to Gu Qingyu's description, I tried to piece together a framework:

The malicious Dai Qingshu deliberately approached my sister, using insinuations and suggestions, leading my sister into depression.

His only purpose in encouraging my sister to commit suicide was to use it to attack Gu Qingyu.

But he didn't expect things to go completely out of control. My sister died in vain and didn't hurt Gu Qingyu at all.

So, he set his sights on me.

As for why Gu Qingyu came, according to his own words, he was bored and hadn't seen such a spectacular live performance in a long time.

He just wanted to come and watch the grandmaster of disguise, Dai Qingshu, perform live.

Gu Qingyu looked down on Dai Qingshu with a disdainful posture, as if he were watching a jumping clown, just like an ant.

He would never have thought that Dai Qingshu would actually kill him.

Dai Qingshu first asked me to do it. With just a light comment, he wanted to hand over the opportunity for me to avenge my sister. I refused.

Gu Qingyu looked at Dai Qingshu, who had been rejected by me, and burst into laughter again.

The next second, Dai Qingshu picked up a syringe and directly stabbed it into Gu Qingyu's carotid artery.

I thought it was just a drug to induce temporary unconsciousness.

Until I noticed Dai Qingshu's hands were shaking, and he was sweating profusely.

"Ling Su, we did it, he's dead."