Marie Heinlein is the older sister of Kain R. Heinlein. She lived happily with her brother and their friend Abel Cameron. Eventually, they grew up and Marie attracted the attention of the crime boss, Geese Howard. They were married, but Marie had to live always hidden from the world, because she would represent a weakness to Geese's enemies. One day, she discovered she was pregnant. She had a boy and named him Rock. So, she lived her unfortunately sad life with her son, until one day, she fell ill and succumbed to her illness. Years later, Kain invited Rock to a King of Fighters tournament in order to tell him the truth about his mother. By the end of such tournament, Kain mentioned that Rock's mother is still alive, directly contradicting what he knew about what happened to his own mother.
In the fan Q & A for the game, creators noted that the confirmation of her death wasn't made by a physician, thus leaving some room for error about her ultimate fate. As such, it may be possible Marie survived her illness after all and is possibly in seclusion.
Although the sequel has not been available to the public, many fans speculate over the real reasons behind her apparent death. There are others who even question Kain's relation to Marie. Though creators have expressed interests in their opinions and alternative views, they have currently not stated anything about such ideas.
There's much speculation about her personality, but nothing is officially confirmed. What is known is that she loved her son and was a rather humble person. She also begged Rock to not bother his father, suggesting that she also knew some of his work. This may be the reason why Marie held no ill will about Geese leaving them to their nondescript apartment.
- Garou: Mark of the Wolves - in a painting in Kain's stage.
- The King of Fighters XIV - in Rock's winquote against Geese
- The King of Fighters: Destiny - mentioned by Rock in episode 11