Certain powerful magical items, particularly intelligent ones, have alignments. Alignment in these cases is not an indication of the moral properties of the item. Rather, it is a means of limiting the number and types of characters capable of using the item—the user's alignment must match the item's alignment for the magic to work properly. Aligned magical items, usually weapons, were created with a specific ethos in mind. the item was attuned to this ethos by its creator.
Aligned items reveal their true powers only to owners who share the same beliefs. In the hands of anyone else, the item's powers remain dormant. An extremely powerful item may even harm a character of another alignment who handles the item, especially if the character's alignment is opposed to the item's.
Aligned magical items should be rare. When an item has an alignment, it is a sign of great power and purpose. This creates opportunities for highly dramatic adventures as the player characters learn about the item, research its history, track it across the country, and finally discover its ancient resting place and overcome the guards and traps set to protect it.
Magical Alignment Changes
A second, more insidious, type of magical item is the one that changes a character's alignment. Unlike the usual, gradual methods by which a character changes alignment, magical alignment changes are instantaneous. The character's personality undergoes an immediate transformation, something like magical brainwashing. Depending on the new alignment, the change may or may not be immediately noticeable. However, you should insist that the player role-play his new situation. Do not allow him to ignore the effects the alignment change will have on his character's personality. Indeed, good role-players will take this as an opportunity to stretch their skills.