While I unlocked this in the Prologue, this may come a bit later than that depending on your preference of gameplay. If you take the time to clear out several waves of enemies for the experience and Kizuna, not to mention the Beat when in Kizuna Rush, then you might very well get this sooner or later, certainly no later than the end of Chapter One if you are doing your best to get all of the Treasure Events and Legend objectives.