There is a planet that fights against the "Dark Will" like Teyvat but is far away from Teyvat. In order to better fight against the "Dark Will", the Etching Tribe signed a "Remembering Contract" with humans. However, when the war reached a stalemate, the contract became useless. The top human beings launched the "White Coffin Project" - since the Etches can resist darkness, they will be hollowed out and made into eternal "humanoid batteries." In the deepest part of the white coffin, the most precious experimental subjects are imprisoned: twin sisters Yun Shu and Yun Juan. On the night when the Etchers fled collectively, the will of the planet, which had been tortured by the "Dark Will", sent its last surviving child, the twin sister Yunjuan, to Teyvat through a deal with Teyvat before its last trace of consciousness dissipated.
