Deep inside the luxurious, mountain-side castle of Canterlot is where none other than the two royal sisters can be found: Princess Celestia and Princess Luna. These two very busty sisters take total advantage of their freedom to be able to roam the halls without a single speck of clothing on, where they let their breasts remain entirely exposed and proudly sticking out from their chests at all times-- a luxury they both fully enjoy in their own personal ways. Problems start to arise, however, when the oldest of the two-- Princess Celestia-- becomes too prideful and begins to tease Luna for all sorts of trivial things, leaving her younger sister feeling agitated and annoyed with all the little bickering. Tensions between the two breastiful princesses escalate, and before long, Luna finds herself abruptly agreeing to hold in her pee for an entire week in hopes that triumphing over Celestia's little challenge will put and end to the mocking once and for all. Soon Luna begins to realize the difficulty of her task, however... seven whole days is a really long time. Even with the help of her pet pony for love and moral support, will she be able to void from emptying her bladder for an entire week? Or will she soon found out just how much a basic bodily urge can be underestimated..

(The reference image for what the two princesses look like can be found as image number #304132 on Derpibooru. If it's not clear already by the description, this is a pee desperation/full bladder themed story..... with alot of boobies too)