Can you help me with the idea of how to make a story which "begins at the ending"?
I think that you might want to investigate the idea of reverse chronology. This method tells the story or seeks to tell a narrative from "the ending as the beginning." In How the Garcia Girls Lost their Accents, Julia Alvarez seeks to do this. Reverse chronology flips the narrative temporal element, making what is in the end the exposition and builds from there. Tarantino used a variation of this in the opening of Pulp Fiction,the result of which was to transform the viewer's understanding of time in the narrative. The use of flashback is critical in this process and through being able to intersperse present with past, the narrative structure and audience interest can be maintained with more openness and a distinctiveness to the work. After examining the concept in detail, I think that you might need to look at the narrative you have constructed and then see how the ending of your work can operate as the opening. Essentially, you would be able to do this with reconfiguring your ending as the beginning and then determining how the work should present its resolution in terms of revisiting it or moving on from it. In this, greater development of your work will be needed as well as a reflection on how reverse chronology could be seen in your final product.