Tristan didn't want to hurt Zhen-Zhen and their twins. But Mheera was so strong that he couldn't take control of his body.
Afraid that he might make a mistake and harm Zhen-Zhen, Tristan made a decision. At that time, Liam also did something that made Mheera distracted.
He tried to pierce Mheera on her right shoulder, hoping that Mheera's soul would also feel the pain inflicted on her physical body.
The moment Liam plunged the dagger into her flesh, Mheera's soul felt the pain. That's the time, Tristan was able to take control of his own body.
He retook the dagger which he was aiming at Zhen-Zhen. And in one swift move, he pierced his own chest using the divine dagger. He thought this was the only way he could stop himself from hurting Zhen-Zhen.
Tristan and Mheera felt an excruciating pain, spreading throughout their system as the divine dagger got in contact with Tristan's flesh.
