Excidium's past is mostly unknown, but three known things are that she was born in Shadoria, a Castrellian country, she had been obsessed with the Pendulums, especially the Heart Of Shadoria, and that a Pendulum (The Soul Of The Void) had injured her heart and cursed her, creating the first of the Weapons Of The Void from her broken body.
Excidium, in her Weapon form, appears as an extraordinarily large Shrapnelblade, and an unnaturally powerful one at that. Her hilt in this form remains the same as other Shrapnelblade hilts, which are longer than the hilts of most other swords and blades. The hilt is blackish-gray. In this form, she has an orb that serves as her heart. This orb has a strange pattern in the form of a crack, which symbolizes her injured heart. Her hilt has purple stripes that wrap around it. Her Weapon form seems to be somewhat retained when she reverts to her Physical Spirit form, as the blade of her form matches her dress in her Physical Spirit form in color, and the orb and stripes upon the hilt match her hair and eyes in color.