As I browsing through the Mugen parts for my civic, I found this
2008 JDM HONDA CIVIC MUGEN RR Brake Cooling Duct OEM
eBay Motors: 2008 JDM HONDA CIVIC MUGEN RR Brake Cooling Duct OEM (item 120253936887 end time May-06-08 22:25:12 PDT)
It looks like a cooling duct for the front brake. Enjoy,