Wedding Rings (Incomplete)
All the wedding rings emit a special aura when you and your partner are near each others (both of you need to wear the same ring). In order to upgrade this rings, you need 'Heart of Sweetness' (obtained from harvesting tree of love [Pink Heart]) & 'Feather + Sweetness' (feather can be bought in shop [Love Tab] & sweetness can be gained by doing couple missions + harvesting tree of love [Blue Heart]).
Here are the lists of each rings, including the sweetness & heart of sweetness that needed for upgrading (data source: touch.3claws.com) :
