Responses
It's the result of all the sucking they did lolll
Inspite of popular misconception by teenage boys (& many men), sucking (or squeezing or pulling) female breasts will never make them bigger. They can swell like any human skin parts but certainly not increase 3 cups larger lol :D.
I don't believe in it either, I was just joking
When the A cup transformed into a D cup in chapter 4