Below may include Non-Canonical info
Hype-Chan is a fan-given name to an unnamed character that appears at the end of Solo Remix. She also seems to have an important role in the new epilogue created for the upcoming enhanced port for the Nintendo Switch: The World Ends With You: Final Remix.
She appears to be a mixture of all of the main characters; Her red skirt and white button-up shirt she wears reminiscences Beat (his white tank top with a red one under it); she has headphones like Neku Sakuraba; she has a plush alike to Shiki's Mr. Mew; her eyes and posture are similar to Rhyme. Her hair color reminds of Joshua. While her appearance remained consistent between the Solo Remix teaser and Final Remix reveal, it's worth noting that her stance and facial expression have both been altered in such a way that they reflect the attitude of Shiki during her Day 6 identity crisis more so than Rhyme at any point.
While considered as the "Proof of A TWEWY Sequel", not much has been said about this character. She's seen after watching the Secret Ending (you will get the "A New Shibuya" Achievement after leaving the Game's Photo).