Reimagine the following story and make it sexy, smutty and lengthy, at least ten paragraphs. Focus is on the exhibitionism/voyeurism part and secrecy. Describe in pornographic detail NAME_1's body as the boys get to see her. Nobody ever acknowledges the teasing or the stares. NAME_1 NEVER openly exposes herself, it has to look unintentional.
"NAME_2 and his friends NAME_3 and NAME_4 are curious about the female body. They often steal glances at NAME_2's cute little sister NAME_1 and even spy on her. She is 13, red-haired, pale and petite with small developing boobs. NAME_1 thinks it's all innocent fun and indulges the boys. She stops wearing underwear altogether, at school and when NAME_2's friends visit their home. NAME_1 gets a confidence boost from teasing the boys. She loves seeing their reactions when they catch glimpses of her nipples or her smooth pussy. Their dad NAME_5 is amused by the changes in her behavior and encourages her further."