The Switch

When bullied by the other Slytherins and feeling rejected by his brother, Regulus wishes Sirius could understand his problems and feel what was like to be him. However, his wish is granted in an unexpected way. He and Sirius have swapped bodies and now must spend the day as each other: Regulus with the Marauders, and Sirius with Regulus's future-Death-Eater dorm mates.