Quite enjoyable! It made me realize diarrhea stories are pretty rare on this site. Naturally I was somewhat reminded of my "Love Hina" fanfic with the stuck zipper, but here it's a very different story.

I like the bit about bowel-rumblings mistaken for stomach-rumblings. "Yuna didn't need to put something in, she needed to let something out." Great line! I also like, "The teeth refused to let go, like a big dog with its favorite toy."

You do a great job of describing Yuna's desperate feelings and her struggle with her clothes. You really make the scene feel urgent. The evacuation itself is especially vivid. It's a long accident, and we get to hear about every phase.

I also enjoyed the scene with Rikku. It's nice to have some female bonding over an accident clean-up. I love how Rikku is just suddenly sitting on the toilet, pissing away.

The one complaint I have is about the very beginning. I think it needs more of an introduction. You don't tell us the setting, and at first we don't even know who's talking.

not much to say, but very nice story ^_^