I remember reading it on Ao3, but when I went back to look for it, it was gone.😭

The plot revolves around Obito and Deidara, who are engaged and travel back to visit their remote Uchiha family in the countryside. However, they discover the family has become a twisted religious group that worships the Sharingan, and Deidara is sacrificed while still trapped in the illusion of a happy life with Obito.