Advent Children has a very immersive and interesting storyline. As we meet up with old and new characters, their own sub-plots embellish the storyline in their own way. The events that fold out of this interweaving of plots makes for a very interesting universe.
Two years have passed since the end of Final Fantasy 7. After the immense struggle between Holy, Meteor and the Lifestream, the world finally seems to be pulling back together and relaxing into a time of peace. Even Midgar, the specific target of Meteor's destructive path, appears to be pulling its act together and creating a "new" civilization. The world, for the most part, appears to be safe.
That is however, until three gray-haired brothers, under the names of Kadaj, Loz and Yazoo appear. With them they bring a new disease to the world: called Geostigma, this disease has unknown side effects, but seems to cause immense pain in the people it afflicts. "Children are the first to suffer", they say. And indeed, many of the children in Midgar have gotten this disease. There appears to be no cure in sight.
One Cloud Strife, living for the most part peacefully after his struggle with Sephiroth, now lives his daily life as a delivery service owner. Back and forth he goes, aroudn the world, delivering packages and items to people. However, he is still in pain over the death of one he loves. He believes that Aeris' death was his fault, and he cannot forgive himself for it. He lives in solitutde most of the time, yet sometimes lives in the presence of Tifa, Marlene and Denzel.
Unfortunately for Cloud, the three gray-haired brothers appear to be after him and their "mother". Determined to find this "mother" of theirs, and relentless in their pursuit of Cloud, these brothers are ruthless to say the least. Cloud must rush to Healin Lodge to learn about the latest happenings, before returning to Midgar and helping to straighten out the situation at hand.
And thus begins the story of Advent Children...