Originally Posted by ickss

Where or how do you get gold-rarity items (i guess it is what you call 4-star item ?), like the one you have just shown ?

When you finish a Character Quest (3 parts).

The borders match up with character rarity borders, so the gold rarity items from character quests are actually 5-star items. The 4-star items are the silver background attack boosting accessories that drop from mid-grade equipment seeds (Warrior's Ring and Warrior's Earrings).