Allen Walker single father and personal assistant to the president of Mugen Corporation lived a pretty ordinary life until one day his life takes a 180 and he ends up much closer to his boss than he would have ever wanted to be. Can he open up his heart and trust Kanda or will he push him away and end up heartbroken?

There's been a break out at the Black Order Institute, the person who escaped? Allen Walker, the most mentally insane person out of everyone in the Institute. The person who's going to bring him back before he hurts anyone else? Kanda Yuu. Will Kanda be able to capture Allen before it's too late or will he lose himself to Allen's madness along the way?

Kanda Yuu and Allen Walker, the once famous Black Heart Duo, have now disbanded and are currently working on starting up their soloists careers. However, what happens when they can't seem to let go of the past and old secrets arise? Why exactly did this dynamic duo break up? Will things ever be the same between these two rock-stars or will fame continue to tear them apart?