Known as Black Silk Underpants in Shadow Hearts, these undergarmets will cut magic/special attack damage in half.
While an Alice exclusive accessory in Shadow Hearts, in Covenant it's for use only with the female members of the party (though somewhat unusally, Gepetto also is able to equip them, though it's Cornelia who wears them). After finishing Covenant, this item will remain in your inventory.
Equiping them does indeed change a character's underwear to black.
The sophisticated choice in undergarments, they have concealed many mysteries. Be sure to be wearing them just in case. They cut Magic Attack damage in half.
Shadow Hearts CovenantEdit
Black, silk underpants that turn people delirious and joyful. Thanks to the special charm of a grown woman, Special Attack Damage is halved.
Shadow Hearts: From the New WorldEdit
For some reason, in From the New World, they are not accessible, outside of using a cheat device. Despite this, they will still change the colour of the Shania or Hildegard's underwear, and cut magic/special attack damage if equipped.