A group of malevolent spirits in Shadow Hearts that live within Yuri's soul. Near the beginning of the game it is shown that Yuri has been placed under a curse by these entities. Yuri battles with their curse constantly throughout the course of the game.
After the events in China have concluded, Alice, Zhuzhen and Keith face Yuri in battle. Yuri has lost touch with reality and attacks anyone who comes near him. After this battle, Alice wakes up in the Graveyard within Yuri's soul. After looking around, Alice notices and confronts the Four Masks and she asks them how to save Yuri. The Four Masks tell her it is impossible to save him unless she bears Yuri's cursed fate in his place. She agrees without a second thought and they question what motivates her to make this decision. One of the Masks even asks: "Could love really exist?" She nods at the Mask and asks to see Yuri again. They tell her that they will allow her to be with him but that he will not be himself and that her life was wasted. She disagrees and walks off. Alice is successful in pulling Yuri out of his madness and Yuri rejoins the party.
During a dream later in the game, she is confronted by the Four Masks again and they tell her that her time has come. They state that she must keep up her end of the bargain. She agrees and walks through the door that they are guarding. Depending on the player's actions during the game, the events that occur inside this room can change. No matter what happens, Alice fights with Atman, If the player did not fulfill the requirements needed, Alice fights alone and dies. However, if the player does fulfill these requirements then Yuri joins the fight and makes the fight winnable. Regardless of what happens in the dream, she awakens alive and well with Yuri concerned about her.
After the final boss is defeated there are two possible endings that are seen depending on whether the above requirements were fulfilled. In either ending, Yuri and Alice are riding a train to Zurich to visit Alice's mother, Alice's fate in her dream is symbolic for her fate from the Four Mask curse. In the Bad Ending, It is shown that Alice passes on peacefully in her sleep while leaning on Yuri during this train ride. In the Good Ending, Alice is seen waking up at the end of the train ride cinematic and Alice states that she intends to live on with her new family.
The Bad Ending is originally canon to Shadow Hearts, but due to the events of Shadow Hearts: Covenant, the Good Ending will later be canon.