"Any card—so long as it exists—has a power that is needed."

tatsuyana:

Yōko gives Yūya the card Smile World, explaining that she had always planned to pass it on when Yūya would need the card and that such a time has undoubtedly come now. She also tells him to never forget his smile no matter where he goes and, that if he does forget, to look at this card and remember today and his father.

Yu-Gi-Oh! Arc-V Episode 053