The R1 Concepts black drilled-and-slotted rear-left brake rotor for 2015–2025 Subaru Outback is listed as a single replacement rotor for the rear left position across those model years. Noted in the source as drilled & slotted with a black finish, the rotor is matched to the rear left fitment of the specified Outback applications.
R1 15-25 Subaru Outback Rear Left Drilled & Slotted Black Brake Rotor