The Sun Shield is the personal shield of Helios. Kratos obtained the Sun Shield within the Temple of Helios, where it was attached to the Sun God's throne. The Sun Shield receives new abilities when leveled up, and it also receives the Helios Reflect ability after Kratos obtains the Primordial Fire within the Caves of Olympus.
After Persephone is defeated and Kratos returns to Earth, Helios takes his shield back.
The Sun Shield is similar to the Golden Fleece used in the later God of War games. Both are powerful, mostly golden artifacts that are worn on the arm and possess the ability to parry and reflect enemy attacks. Unlike the Sun Shield, the GoW version of the Golden Fleece is based on a real myth, but lacks a direct affiliation to any specific god.