A flat chested student goes to bed after working on her science fair fungus project, only to wake up the next morning with enormous breasts and a cup size in the second half of the alphabet! "Where did these come from?!" she asks, astonished at her staggering rack.

But it doesn't stop with her! Within a day or two all the girls in school are experiencing rapid, massive breast expansion! Somebody call the CDC, because there's a big-tit epidemic!

Fortunately for our protagonist, her direct exposure to the fungal spore causes her to keep growing, bigger and bigger, and no one else even comes close to her eventual, supremely big titted proportions!

That's the plotline from Spore, a comic available for digital download from the BE Story Club. Growing tits forever!