[Nayuzaki Natsumi] Aheiki! Shoujo Seikatsu Shidou page 53-98 [xinsu]

A shy, studious schoolgirl with an impossibly busty figure spends her summer buried in books—until a smiling upperclassman draws her out with promises of conversation and things spiral beyond her control. A leaked video of her first time becomes leverage, and what starts as coerced groping escalates into relentless group sessions where her huge breasts and tight throat are passed around without mercy. By the end, the timid student is unrecognizable: a tanned, bleach-blonde gyaru who gleefully invites crowds of men to use her every single day, her transformation complete.