Sombra, the dreaded King of Darkness, was defeated and his body shattered, but his dark soul survived the return of the Crystal Empire and went into hiding. Some time later it found a path between worlds, a mirror portal, and arrived in a place called Hueco Mundo, where it gained a new body to start a new life. In the process Sombra loses his memories and becomes a shell of his former self, searching for something that he knows that he lost while having no idea where to find what he was missing.
Along the way he somehow finds his way to Karakura Town, into the hands of Kisuke Urahara, and learns more about his new body than he could have learned on his own, before coming into contact with Ichigo Kurosaki and his small group of friends. From there he starts an epic journey to help them save another friend from a terrible fate, fight the people that were in their way, and face an evil that was hiding in plain sight at the same time... along with finding out what happened to his missing memories.
(Bleach/ MLP Crossover)
(Part of the Universe 13 story series, though reading the other stories is not required)
(Also, the story will not include the Fullbring or the Thousand Year War Arcs)