There are extra characters in this game, and here is how to get them.
Code- Effect
Asuka - Beat Daichi's story
Gyamon - Beat Guy's story
Koki - Beat Hibito's story
Shura - Beat Kairu's story
Major Titles
Complete the indicated Story mode to unlock the corresponding title.
Earth Major: Earth Hero's Story mode.
Elec Major: Thunder Hero's Story mode.
Fire Major: Fire Hero's Story mode.
Ice Major: Kyle's Story mode.
Water Major: Water Hero's Story mode.
Shadow of Darkness bonus quest
Successfully complete Story mode with all default characters, with the "Fire Major", "Aqua Major", "Rock Major", and "Elec Major" titles to unlock the "Shadow Of Darkness" bonus quest at Synethesia.
Unlock Zeke
Beat Story Mode with all the main characters, earning the titles of "Fire Major", "Aqua Major", "Rock Major", and "Elec Major". When you do, the hidden quest "Shadow of Darkness" will be available at Synethesia. After you complete all the quests, including "Shadow of Darkness", Zeke will become available to use in Wireless battles.