Puzzle Pieces (Soul Eater Fanfiction)

A lamb. A rose. The YinYang. A rose. A skull. A flame. An orb.

These are all pieces to a puzzle. The victims of a maze. The skull's decision whether or not to kill the lamb. The rose seeks revenge on the yin and yang. The flame and orb teams up with the rose to find the ones they love. But in the end, everyone shall kill the ones at the end of the maze once they complete the puzzle.

Why are they chosen as the pieces? Why is she screaming apologies? Why is he pointing a gun at her? Why is she going crazy? Why is she sacrificing herself? Who are they?