Finding Minerva

The Soul Imprint Seed swiftly germinated within Rolce, seamlessly merging with the vessel's original soul and gaining complete control of the body.

This process resembled demonic possession but with a slight twist.

It meant that Eren didn't have to expel Rolce's soul from his body to take control; nor did he need to fuse the Soul Imprint and Rolce's soul into a singular being.

Thus, additional steps like adding Simbelmyne Flowers and Astral Projection Potion into the process were unnecessary, unlike Eliza's approach in the Lazarus Project with the help of Leela and Layla.

Of course, Eliza, in a way, ended up being possessed by Lady Zee's consciousness anyway because of Eren's silent intervention in the Lazarus Project.

One could say that Eren had developed a lot of expertise for his Rank in dealing with matters related to the souls.

As for the pseudo-avatars AKA the perma-clones?