Everyone knows Nico Yazawa. On the other hand, nobody knows Seishirou Yazawa. Born between Nico and Kokoro, Sei is a simple person. After reuniting with his siblings after five years, he can't help but think about making at least some significance in his own life. Determined to maintain his lifestyle, he fails to realize that his 'simple life' was nearing its end.

The game's changed... What people once knew as a boring themed mobile game shook the world and became one of the most endearing rhythm games of all time! The Dual EX mode, a system where players can bring their idols to life, has become so popular around the world. However, it isn't all fun and games. A fiery showdown between unrelenting hearts begins!