18+ Osananajimi no Mune ga Ookiku Natta no wa Ore no Sei kamo Shirenai

In his second year in high school, Yamato has a big problem. His best friend from childhood, Honoka, has a certain stress-induced illness that made her chest huge. Now he struggles to protect her from those who look at her with predator eyes...!?

(Source: Shueisha, translated)