Stories of the Great Crusch-sama Prologue: Oath Chapter (クルシュ様偉人伝序幕、誓いの章) is a shop exclusive limited edition short story. This was later adapted and included in the Re:Zero Ootsuka Shinichirou Art Works Re:BOX.
Felix is training with a sword in hopes of becoming a knight, however no matter how much he trains, he is getting frustrated that he doesn't have any skill and is unable to improve with the sword. Crusch arrives and asks Felix to lend the sword he is using so she could train, accidentally showing that she is far superior to him. While at it the duo talk and Crusch reveals that sometimes it feels like her father wished she were born a man, as he keeps telling her to give up on the path of the sword and to be more feminine. Wishing for Crusch to be happy, Felix yells that if that would be what is troubling her, he could be the woman she will never be, while she can be the swordsman he will never grow to be and both would succeed where the other would not (he feels a bit embarrassed by what he said on the spur of the moment). After an awkward silence, Crusch burst outs laughing and agrees, removing her ribbon and placing it on Felix. She says that if Felix no longer wishes to be the woman she will never grow to be, he can give it back to her, as she would give back her part of the agreement if he ever wishes to. In the end, Felix replies that he would never do such a thing and would follow this path for her forever.