Well, without more information about this Marx Kirby sad story, it's really difficult to tell. It could be about a relationship between Marx and Kirby that went wrong. Maybe they were friends and had a falling - out over something important, like a betrayal of trust. Or perhaps it was a love story that ended sadly, with heartbreak and disappointment.
I'm not sure specifically which 'Marx Kirby sad story' you are referring to. There could be many people named Marx and Kirby. It might be a story within a particular community, family, or a fictional context that I'm not aware of without more details.
Since I don't have enough information about this Marx Kirby sad story, it's hard to give a definite account. However, in general, a sad story could involve loss. Maybe Marx lost Kirby due to an accident or an illness. Or it could be a story of unfulfilled dreams. Marx and Kirby might have had big plans together, but for some reason, those plans never came to fruition, leaving them with a sense of sadness and regret.