Speaking in an interview with Nintendo Dream magazine (via FF Reunion), Kingdom Hearts and Final Fantasy Versus XIII boss Tetsuya Nomura shared a brief hint concerning a possible continuation to The World Ends With You.
The article specifically calls out the character Rhyme from TWEWY, who did not have any lines in the original game. She does however, speak in Kingdom Hearts 3D, which Nomura decided to include "out of consideration for the future of the series."
The director also hinted toward a possible sequel saying, "Right now it's not possible for me to say anything... (laughs). There could be something."
Having originally released in 2007 in Japan and 2008 overseas, it's been quite a while since the original launched on the Nintendo DS. KH3D's cameo is both welcome and hopefully an exciting hint at things to come.