Puzzle Pieces

Anzu and her friends have worked for Sugoroku Mutou in his Game Shop for several years now. So, naturally, they've met his grandson, Yuugi- a quiet, drawn-back Boy their age. He doesn't go to school, doesn't talk... he just sits there, with his little Treasure.

When Sugoroku is forced to leave his grandchild for a two-week span, he beseeches his employees/friends to stay at the shop, and keep an eye on Yuugi while he is away.

Is there nothing to be revealed about the boy with the golden puzzle in the short span of time, like they expect? Or is there more to him than meets the eye?