I’m not entirely sure how much I believe the theory of Alain being a Fatui Harbinger and Sandrone being a puppet replica of his sister.

In the World Quest Series Questioning Melusine and Answering Machine, we encounter a mysterious Fatui agent interested in machine intelligence specifically Curve, a lie-detecting machine. This mysterious Fatui agent worked with Jenck, an editor from the Steambird named Baulande. During their collaboration Curve ends up dying, and Jenck is subsequently punished. His tongue was cut out and his mind was broken by a certain sadistic Fatui Harbinger.

This act seems too cruel for someone like Alain Guillotin to commit, so personally I’m not too too committed to the theory.