Ram's Sister is Complicated (ラムの姉心は複雑) is a shop exclusive limited edition short story. This was later adapted and included in the Re:Zero Ootsuka Shinichirou Art Works Re:BOX.
After the mabeast incident, Rem is getting very attached to Subaru a thing that is disturbing Ram as time goes by. She grows harsher at Subaru due to this, as she always wished that someone would appear to control Rem's insecurities and make her smile truly again, she is only disgusted to think that person is being Subaru. While inspecting a work Subaru is doing and being annoyed by these thoughts, she overworks herself trying to be better than Subaru and then she collapses. This causes Subaru to take care of Ram in her room as Rem is too busy to do so, much to Ram's annoyance. In the end Rem visits after finishing her chores and notices that Ram slept while holding Subaru's hand, saying that this rare scene must be because she finally accepted Subaru, with Subaru replying he was not so sure, as she had insulted him from the beginning to the very last minute until she asked to hold hands before sleeping.