Oracle's Robe

The Oracle's Robe is a Robe-class piece of armor found in.

In
The Oracle's Robe is found in a chest in Tunnel Ruins, in a room accessible from the left path down, and is hidden as a statue and can only be opened by casting the Reveal Psynergy. While a robe, it can only be equipped by female Adepts, meaning Mia in the first game and Jenna and Sheba in the second if the robe is transferred into that game.

While an entirely valid piece of gear for Mia to wear at the end of Golden Sun due to its ease of discovery, it is probably not the best possible body armor for her to wear, since the Feathered Robe is strong enough that a dedicated player would do well to earn two of them and equip them on both Ivan and Mia. That should not discourage less dedicated players, though, for this is still a very powerful piece of equipment that might remain equipped even when the first game's party is transferred into The Lost Age to take part in that game's late-game content. At the very least, it is a substantial upgrade to the Blessed Robe that just so happens to have the limitation of not being able to be equipped on Ivan.

Cultural Reference
The Oracle's Robe's original name in Japanese refers to Oto-hime, the princess of the undersea palace of Ryūgū-jō and the daughter of Ryūjin, the dragon god of the sea in Japanese mythology.