Io Nanba

Io is the elder sister of Rio and Hokuto Umeda and is the mother of Minami Nanba. She is introduced in the third volume of Hana-Kimi, when she requests that Hokuto work at her inn. Her brother instead offers Mizuki, Sano, and Nakatsu in his place and Hokuto leaves before she has a chance to object. She discovers Mizuki's secret while she's changing out of her clothes and later provides Mizuki with more comfortable vests to cover up her developing body. (Source: Wiki)