Reika Kuze was preparing for the Impalement Ritual by etching all her grief into the Mirror of Loss so that it would not interfere with the parishioners. Much of her pain and suffering was concerning the absent Kaname. It is made by her desire and longing to see him for at least the final time.
The Mirror of Loss is only obtained during the thirteenth night by collecting five shattered fragments that forms it. These scattered fragments are in various locations that has relation with Reika's emotions and pain.
The Mirror of Loss is also recovered by Miku from the hanging prison along with the first tattooed diary.
❛I engrave my feelings, my holly, in these mirrors and break them here. Because they are my feelings alone.
But if it were in my power, I would see him one more time.❜ — Reika Kuze.