Why did Thyme Tu Su die in the final ending of Legend's Sword?

Because when the protagonist was very young, when Ouyang Shaogong and Lei Yan robbed Gu Jian of silence, he was sucked away by a jade cross ... So, Susuma combined the sword spirit in "Burning Silence" with Susu ... and saved Susu, which also led to Susu becoming a monster at any time ... Finally, Ouyang Shaofu used the lives of coastal cities and hostesses to coerce Tu Su to unlock the seal ... only three days later. .....