Most player's characters have favored weapons and or items, and certain approaches to problem solving. Your players should have individual toys and affectations.
Unbeknownst to them write down a particular skill and maybe a feat associated with that individual character along with one or two favored and unique items. When their new characters happen upon their old relics. They get a special sort of gift.
Like if the warrior was particularly fond of saying, "you're with us or against us" and killing everyone against them, the new owner of the sword might get an intimidate bonus, unbeknownst to them, whenever they try to intimidate someone or something with their hand on the sword, or any part of the sword is visible to the other party. Slowly the characters might realize the true, and very cool power of the relics, and maybe unlock or awaken other powers.
I would probably go with 1 signature skill, that is initially available, but unknown to all but you, and 1 signature feat that must be 'awakened'. Again, they get the skills and feats from the item, should they loose the item, they loose the boons. I'd even let them take feats that had the feats granted by the items as prerequisites, but then they'd loose two feats if they lost the weapon.
Like if one of the players was notorious for rolling absurdly high damage or criticals, especially at climactic moments, their weapon, or item might grant improved critical.
Stuff like that.
