It's most likely a TVS (transient voltage supression diode) with an Onsemi branding, but no standard catalog part. The fact, that the case is apparently crashed makes me think, that the device finally disconnected the short current during the polarity reversal event. In this case, I fear that more parts are permanently damaged.
The TVS has to purpose in normal operation, so you can desolder it without replacement, if you're sure about the correct power supply. Try if the HDD is still operational. If not,there isn't much hope.
If you need to recover the data, there may be a chance to replace the controller board from a same type device.