Preheat oven to 400 degrees F (200 degrees C). Line a baking sheet with foil.
Season the pork tenderloin with salt and pepper. Heat olive oil in a heavy skillet over high heat until the oil shimmers; gently lay the tenderloin into the hot oil. After about 1 minute, gently loosen the meat from the bottom of the skillet, if necessary. Cook until the pork is seared a golden brown color, about 3 minutes per side. Transfer the pork to the lined baking sheet.
Roast the seared tenderloin in the preheated oven until a thermometer inserted into the center of the pork reads at least 145 degrees F (63 degrees C), about 15 minutes. Remove the pork from the oven and allow to rest for 10 minutes before slicing into medallions.
Cook the plums, balsamic vinegar, brown sugar, honey, and blueberry juice in a small saucepan over medium-low heat, stirring often, until the plums are soft, about 10 minutes. Transfer the sauce to a blender and blend until smooth. Return the sauce to the saucepan and simmer until reduced and thickened to the consistency of apple butter, about 5 more minutes. Spoon plum sauce over the sliced pork to serve.