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One of the presences inside Lucia Mar, said to be with her and present only when the dogs are close.
When Diah surfaces to plead with Carl, she explains the arrangement inside their shared body: "Lucia is with Alexandro. And Alexandro is only here when the dogs are close."
The implication is that Gustavo 3 and his counterpart anchor both Lucia Mar and Alexandro to the surface, and that when the dogs wander off, Lucia fades and one of the other children in the dark takes a turn seeing the light.
A hidden presence sharing Lucia Mar's body, tied to the proximity of her rottweilers.
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