Magic Mirror Shield of Depravity is a magic item described in Monster Girl Encyclopedia World Guide - Side II.
Guide Book Entry
Shedding light on the books left from the ancient times of the Kingdom of Lescatie, I learned that in the past there seemed to be a treasure called the Great Sacred Mirror, which was created and blessed by the Chief God Who created this world himself. This artifact was in the hands of the Church, and if a person of the right qualities was found in front of it, it reflected him in the image of a hero, which was the likely future of that person after receiving the blessing of the Chief God. The Order used the mirror to seek out talented individuals and to gather heroes into its ranks to increase its influence. At some point, however, the Sacred Mirror was lost.
And even now the Order is still looking for this lost artifact. But when a military fortress, Castle Salvarision, was built on this site, then Priest Noscrim, who had enormous power in Lescatie, secretly obtained a "sacred shield" made from part of the lost Great Sacred Mirror. With it, even in secret from the Order, he sought out heroes whom he used as his pawns to expand his own power and influence. Apparently, his possession of this shield was a secret of which few knew, even in Lescatie itself. Nevertheless, I am not interested in the ambitions of Priest Noscrim, who outsmarted even the Order itself, gathering heroes to his side, and was the de facto real ruler of Lescatie. I'm only here to tell you about one of the treasures Noscrim left behind, the "Sacred Shield," and how it has changed in the current mamono realm of Lescatie. When the "Sacred Shield" ended up in the hands of Druella, it was charged with her powerful magic power, and is now given to the dark knights under the name "Magic Mirror Shield of Depravity."
The nature of this artifact has been transformed in fiendish fashion: it is now a powerful equipment that invites the beholder of this shield to debauchery. The shield now sees both the qualities and desires of the person who looks into it, and in the reflection will show him his appearance after he would have been monsterized. A girl who has turned into a beautiful and obscene creature in the reflection of the mirror will be enchanted by her own appearance. As she continues to look in the mirror, she will become the same as in the reflection, in other words, she will turn into a mamono. In addition, this mirror is also said to absorb any magical powers. In combat, the magic mirror mounted on the shield "absorbs" all the mana that the enemy emits, and when "the reflection of the enemy changes its race in the mirror," it will cast off that magical energy as mamono mana. To this day, this shield is used by the dark knights as an "anti-hero" equipment during the Order's large-scale operations "to save Lescatie," which have been conducted many times. Because of this, many heroes were turned into monsters by this shield. The stronger the virtue of the man on the other side of the shield, the stronger the feelings that define him as a hero hidden in his chest, the more significant the magic of the magic mirror manifests its power and invites the heart of the enemy to be corrupted. And despite the fact that it is only a fragment, just looking at this shield once, I felt its enormous power. Probably when the mirror was whole, when it was the "Great Sacred Mirror," one could feel all the greatness of the Chief God's Church.
If all the fragments fall into the hands of monsters and they are restored as one great mirror....
...I can't help but think of the possibilities of such a future.[1]