From their website:

Hello World & Hello Kitty's 50th Anniversary!

You can never have too many friends, so bring them out to Fenway Park for Hello Kitty's 50th Anniversary. We're celebrating with red bows and the Boston Red Sox as they take on the Toronto Blue Jays on Tuesday, June 25.

Everybody say Hello Kitty and join us for an evening of throwing kindness like confetti. Ticket holders who purchase through this special offer will receive a limited-edition Hello Kitty bobblehead wearing a Red Sox jersey with the 50th Anniversary logo.

For questions or groups of 15 or more, please contact the Red Sox Ticket Office at ticketoffice@redsox.com.