I'm not familiar with how yukata work, but if I had to take a wild guess I'd bet that it's not a garment that's can fit very well on a figure with so much more breast than waist. The towel then would equalize the difference, allowing the garment to fit the breast without draping too loose on the waist.
It looks to me like Ai wants to pad out her obi to flatten the difference between her stomach and her bust, as having a prominent bust not only makes it harder to wear a yukata (like XionGaTaosenai said), it's also frowned on aesthetically, as far as I know.
So she wants a towel, but Volleybu-chan is having none of it.
Also, the artist commentary is a reference to the movie [Uchiageta Hanabi, Shita kara Miru ka? Yoko kara Miru ka?] (Do You View Fireworks From Below Or From The Side?). It's getting a remake soon, so I guess it's on Himura's mind.
Both Yukatas and Kimonos are ment for slimmer figures. Due to the old japanese idea of beauty being slim figures. So having Big Breasts works againsts that idea. So the point of the towel is to flatten her out and equalize the front.
Both Yukatas and Kimonos are ment for slimmer figures. Due to the old japanese idea of beauty being slim figures. So having Big Breasts works againsts that idea. So the point of the towel is to flatten her out and equalize the front.
I always thought that they're meant to conceal women's body curves instead for modesty's sake.