The boy is Seymour Krelborn. He was found dumped in the trash by a homeless man; his mother never came forward. The baby was given to the first family that would have him. From them he took a name, basic social skills, and a few good memories.
At age six, the Krelborns sent him back to foster care. He was shuffled from house to house - the adoption that stuck was Gustav Mushnik, a successful florist. That success faded when the newest mega-store opened up. They had to leave the apartment and relocate the shop to the bad side of town - and in LA, that side is Skid Row. They slept in the basement and lived little better than the bums on the sidewalk.
Seymour grew up shy, nice, nervous, and mad for flowers and plants. His dad treated him more like an employee than a son - a klutzy, inept employee at that. Unfortunately, as poor a help as Seymour was around the store, he wasn’t good at much else, competent at neither schooling, sports or friendships.
When Seymour was twenty, a girl came into the shop looking for a job. Her name was Audrey. Mushnik hired her because she was pretty and she'd blow him free of charge. Seymour was instantly smitten with his new co-worker. Once he saw past her body, he still liked her. Audrey liked being treated like a human being instead of a whore. But she also liked getting out of Skid Row, and Seymour couldn't give her that.
Some unspecified day, there was a total eclipse of the sun, and a strange humming sound like something from another world. Seymour found a strange plant and took it home. The plant attracted business to the store and some media attention.
It also ate blood. Seymour fed it his own until one day that wasn't enough. The plant said "Feed me."
Now, sweet little Audrey was dating a fella with money and certain sadistic tendencies: a dentist. It wasn't hard to ambush him. It was more difficult to pull the trigger. It was extremely difficult to chop the dentist up and feed the plant piece by piece.
Seymour struggled with his guilt as he moved in on Audrey. She reciprocated his feelings. The plant went silent again and continued to bring in money. Then Mr. Mushnik put a few facts together and realized what must have happened to the dentist. Seymour was going to go to jail. The plant whispered in his ear - and Seymour talked Mr. Mushnik into the plant's mouth.
And it's about this time that 94% of the population died. The plant and the money it provided weren't very important. The plant could figure out that something was up. It attacked Audrey. Seymour rushed in. He broke his wrist fighting the plant, but he managed to get her out with only light wounds to show for it.
It wasn't hard to siphon gas from a car and burn the store - and the plant - to the ground. Audrey's mother had died. Seymour had no one to miss. They had the whole dead, rotting, empty world to themselves. They decided to get out of Skid Row together.
They were heading east, going to see if Audrey's father was still alive. Seymour learned quickly to keep his pistol with them as they traveled. His wrist didn't heal well. There was a scare when one of her wounds got infected; her body fought it off, but it left her weak.
Audrey's father doesn't actually live in Wisconsin. That just happens to be the state where Audrey disappeared. One night Seymour went to sleep with her beside him; the next morning, Audrey was gone. If she left, she left without a note or her backpack full of provisions. If she was taken by force, whoever took her left no sign and stole their car.
Seymour searched and didn't find her. Waited for her and she didn't come.
So now he's wandering into Hell. He hopes she's here.