When Madison Grail was killed by a particle accelerator through the head, she thought "KLAXBCLAILOEJAFK" and crumpled to the ground.
But when Death came to reap her soul, his leg got tangled in her particle accelerated hair on the way out, and he falled on the floor, breaking his USB Flash Drive of Souls. Chaos ensued. Many things (but not all; only a fool keeps everything on a single flash drive) that should have been dead were suddenly not, like dinosaurs and chivalry. This, of course, included Madison. Does it make sense that even though the body is dead/gone, something can come back to life if its soul is freed? No. Shut up.
So Madison was excited to be alive again, but Death was not. In a fit of irresponsibility, he blamed her for the current situation and demanded she correct everything and make all the dead stuff dead again. And she's like "how" and Death was all "ASLFKADOVJEOIF" and gave her a black lumpy egg which hatches into DEATH-KUN which is basically just a dumpy offshoot of himself to assist her in doing this stuff. And then big Death fled the scene.
Also available as a pdf.