Who is the boy listening to Zorua story in Castelia city?

You're likely referring to the anime series! In the anime, the boy listening to Zorua's story in Castelia City is Ash.

Zorua, disguised as a young boy, tells Ash a story about a lost child and how it was saved by a kind stranger. This story was actually a ploy to lure Ash into a trap, but ultimately, Ash sees through the deception.