Life & Death: As Vague As Evening Fog As Real As Morning Dew
Eren started living Goro's life in a trance.
He was digesting all his memories, experiences, elemental attainments, class-specific nuances, weapon comprehensions, and spells. He was removing Goro's influence from all that was his, turning them into his own experiences.
The death element.
This was the element Eren had no prior knowledge of. He had never fought a necromancer in his previous life. Death element wielders in other classes were also very rare. Thus, the introduction of this element was a completely fresh start for the butcher.
Eren continued to live Goro's life in his mind while slowly building up his foundation in the element. Once that was done, he started absorbing class-specific nuances and spells. He discarded his day-to-day mundane memories and other experiences he had no use for, retaining only the most useful ones he could make use of.