Lulu is a girl that was left in the Kamiyama's yard as a baby, she was taken care of by Tenko and Samatarou as if she were their child. It was later revealed that she was the name of a doll that Ai owned, and because of God, she was made human after the doll with the same name fell of a pedestrian bridge.
She first appeared as a baby, and rapidly got older, and grew hair (which is black), and got taller.
Because of her odd growing, she has been seen at almost every age, here is list of her personalities from each age group.
Baby: because she was a baby at the time she was very happy and liked being around Tenko and Samatarou.
Kindergartner - Elementary schooler: She began to learn words even though none were taught to her, and she grew hair.
Middle schooler: she started talking clearer and her hair grew longer.
High schooler: she stopped growing rapidly and remembered everything about her and Ai.