Holy Shroud's Promise (聖骸布の約束 Seigaifu no Yakusoku ) is the name of a charm introduced in Corpse Party -THE ANTHOLOGY- Sachiko no Ren'ai Yūgi ♥ Hysteric Birthday 2U.
Little is known about the origin and the details of the charm. It is believed to carry one's wish and transfer one's negative emotion and misfortune to pieces of cloth, then wash them away. If the charm fails, the participants would be sent to Heavenly Host Elementary School.
However, it is implied that one must also make a deal with an entity called the Holy Shroud's Evil Spirit before performing the charm, though the details are unknown.
Sachiko Shinozaki mentions that the charm's name appeared in her mother's notebook. Sachiko hates that the premise of the charm is similar to that of Sachiko in the Everafter, allowing only the latter to exist and destroy all the other "copies".
Each participant must write his or her own name on a piece of white cloth, and then tie the tip of the cloth with the other participants' tightly. The cloths then are released into a river, and participants must hold each other's hand and pray for their wish.
If the piece of cloths get stuck somewhere midway, the charm fails.