The memory fragments

[Lucy's POV: ]

The memory fragments were monsters that contained a set of memories of their past selves, the negative memories to be more precise.

They were a kind of undead that were only born from people that had endured a variety of deep traumas throughout their lives. 

Born from not the body of the dead, or the soul, or the skeleton, they were a condensed form of negative memories that had taken on a dangerous, complete spiritual form that made any kind of physical or magic attacks useless against them.

'They were a rare kind of unkillable monsters.'

They did not have a physical body so physical attacks wouldn't work on them and since they were only a cluster of specific memories with a unique will of their own, they also practically did not have a body that could be affected with a simple kind of magic.

'They were free and eccentric in nature. Creatures that were like an evil child in nature.'