Slow growth but not too slow... The growing has not to be everything in the story to be really interesting, but the "main" thing... Looks good to add the reasons of the process (magical power, potion, sucking them...) and if it's forced or not...
Sex or not? Uhm... I think sex may be, but absolutely without violence... And if a BE process is, sex should interests above all the growing breasts. The ejaculation may happens at the same time of an unexpected milk squirting from growth boobs!
And milk from growth boobs may have the power to produce growing on other women's boobs... So including lesbian scenes beyond classic man/woman...
Need only a few fantasy...
