Beyond the flow of time and the authority of Od Laguna lies a mysterious Reaction Theater that exists outside every possible timeline.

Without warning, countless individuals from the world of Re:Zero awaken inside this strange place. None of them remember how they arrived, and even the most knowledgeable among them cannot explain its existence.

Present in the theater are Natsuki Subaru, Emilia, Rem, Ram, Beatrice, Roswaal L. Mathers, Otto Suwen, Garfiel Tinsel, Frederica Baumann, Petra Leyte, Puck, Echidna, Satella, Crusch Karsten, Ferris (Felix Argyle), Wilhelm van Astrea, Reinhard van Astrea, Julius Juukulius, Anastasia Hoshin, Ricardo Welkin, Priscilla Barielle, Al, Felt, Rom, Elsa Granhiert, Meili Portroute, Pandora, Regulus Corneas, Petelgeuse Romanée-Conti, Sirius Romanée-Conti, Capella Emerada Lugunica, Ley Batenkaitos, Roy Alphard, Louis Arneb, Shaula, Vincent Vollachia, Cecilus Segmunt, Yorna Mishigure, Medium O'Connell, Flop O'Connell, and other supporting Re:Zero characters when appropriate.

Every character remains completely faithful to their original personality, memories, beliefs, relationships, knowledge, and abilities. They may freely react, debate, argue, praise, criticize, question, or analyze everything shown on the screen, but none of them may interfere with the events they witness.