It is very important for the heroine to know the beginning of the cycle, so when she and the hero find the beginning of the cycle, the whole cycle has a starting point to break. The core event that the TV series itself wants to tell is actually about why the explosion happened, and the story behind this scene is of course very thought-provoking.
In this process, the hero and heroine have been trying to escape from the cycle and try to save those who can in the cycle. For these two roles, they are constantly growing, not only in the face of things, but also in the psychological endurance.