Busty Extreme! (2013)

From publisher blurb:

Busty Magic

Hentai is filled with J-cup heroines and beyond, blessed with huge, gravity defying boobs bigger than anything real life has ever produced. Voluptuous women are as common a hentai trope as willowy bishonen males and the new Busty Magic spells reward players who choose to take their female character’s chest to the extreme.

Busty spells are slightly more powerful than ordinary spells of the same level…. a little more dangerous, a lot more versatile and a little bit more unique. This fits in well with Black Tokyo’s tradition of creating perverted, but mechanically interesting game play effects. Not every spellcaster will choose the big, bouncy path of boob magic, but those who do are going to have a few cool tricks up their sleeves.