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In Pokemon Colosseum, Rui is the only person who is able to see the aura emanating from shadow pokemon, which is otherwise invisible to everyone else, which of course leads to her getting kidnapped by Cipher in an attempt for her not to interfere with their plans.
However, over the course of the game, it is not ever explained why exactly she is able to detect these shadow auras and no one else.
Why do (You) think Rui has the ability to see shadow pokemon?