Red Velvet's Joy, and Billlie's Tsuki are most recent guests in Self-On (Cell Phone) KODE Series.
Members of Red Velvet and Billlie created hidden identities to engage in interesting and fun chats.

Cell Phone KODE is a series in which artists and entertainers appear with a 'hidden' identity, and then they start to text through the app to get to know each other a bit, ask questions, and then finally to guess who is on the other side of the chat.