Mature first appeared as Rugal Bernstein's secretary in the King of Fighters'94. She was not seen during the 1995 tournament, having been replaced in that role by Vice, but resurfaced in 1996 to team up with Iori Yagami and Vice. The two women had been assigned to spy on Yagami, but ended up joining Iori, turning on fellow Hakkeshu member Goenitz in the final battle.
However, their betrayal led to Iori being overwhelmed by his Orochi blood, and he violently attacked his teammates, leaving them for dead.
Mature mysteriously resurfaced for the final chapter of Ash's saga and joined Iori's team. How she survived the attack remains unknown, but she is now wearing an eyepatch, certainly a consequence of Iori's assault.
There are subtle clues hinting at a possible romantic relationship with Rugal.