I know Eva gave them both their necklaces just as Sparda gave them both their swords, but do they actually do anything special like protect or heal them? Vergil really seemed to want his back in Downfall after his "better half" took it, and Dante has never lost his even throughout his troubled childhood.
Do the necklaces do anything special for them, or is it just sentimental value? --- Sabretooth: "End of the line, runt. Got any last words?" Wolverine: "Yeah, two." SNIKT!!! SNIKT!!!
Did you even play the game? The necklaces were very important plot points. Near the end, it's revealed that the red jewel in them is in fact a capsule of aglaophotis, which Dante drinks in order to abort Mundus's baby.