Ristaccia is a seemingly magical jewel that lay in the Ouroboros Ark when it "fell" into the land of Aria Te'Laria. It is depicted as crimson in the written chapters, but usually seen in tones that approach fuschia or light purple rather than blood red, even though the actual colour is debatable. Its original shape is unknown, but it was cut into eight pieces that are shown as being ovoid in the Overture PV. It possesses incredible powers, the most notable of which being the gift of self-awareness and emotions to any being that comes into contact with it. Under its influence, those beings will grow to build societies and cultures. It can also be used in a weapon to make both said weapon and its wielder way more powerful. Because of those powers, the jewel also causes conflicts and ultimately leads to the demise of the beings it once helped.
Ristaccia is, in reality, just an alter-ego of L'erisia - and through this form, she is able to control the entirety of Aria Te'Laria, since they cannot live without their emotions or qualia in general.