It’s Just Revenge, Why Is Master Qing Leng Broken?

[Fantasy imagination + yandere + blackening + revenge + counter-routine] After his rebirth, Gu Jianchen is full of hatred and vows to end the life of Xie Qinghan, the number one person in the immortal world, with a cup of poisonous tea at the apprenticeship ceremony, making her pay for the sins of her previous life. But when Xie Qinghan, with a smile in his beautiful eyes, drank the deadly poisonous tea without any harm, Gu Jianchen's world instantly collapsed.
"Good disciple, I got tired of this 'Erotic Soul Powder' as a master a hundred years ago." Her voice was soft, but it was like thunder exploding in Gu Jianchen's ears. Immediately afterwards, the revenge system prompt sounded suddenly: the assassination failed, but it unexpectedly triggered the master's "joyful" emotion and rewarded "sword mastery"!
Why does this master, who is supposed to be cold and noble, behave so strangely? Faced with the apprentice with evil intentions, she not only did not punish her, but defended her shortcomings in public, declaring domineeringly: "My people are also yours to discuss?" What kind of secret is hidden behind all this? Where will Gu Jianchen's road to revenge go?