This article is from the Final-Fantasy and other Square Soft Games FAQ, by firstname.lastname@example.org (Nick Zitzmann) with numerous contributions by others.
These MAGI, when equipped, can be used as items in battle. In battle,
scroll down the person's inventory, and a ninth item - the MAGI - will
appear. You can use it as an item now.
The Masamune MAGI can be used as a sword.
The Aegis MAGI works the same way as a shield, except it covers the
entire party instead of just one character.
The Heart MAGI will revive a stunned character in battle, but it only
works once until it is recharged at an inn or with a tent.