Clumsy Duo is a shop exclusive limited edition short story. This was later adapted and included in the Re:Zero Ootsuka Shinichirou Art Works Re:BOX.
This story happens during the first loop from "Satella's" point of view. It showcases what are her first impressions of Subaru, like how she thinks he is a weird person but also funny and also her guilty consciousness for tricking him with her lie (Puck even teases her due to it). The story follows up until their first death in arc 1 happens.