Mizuho Asano

is the older sister of Keigo Asano. She is the 24th student body president of her grade at Kuuza Daiichi High School and evidently works to handle multiple school affairs, including the local Kendo club. She likes guys with shaved heads, which is why she lets Ikkaku Madarame and Yumichika Ayasegawa stay in the Asano family's house. In the anime, she is often involving Ikkaku in many comic situations. During a kendo tournament she forces Ikkaku to participate, only for it to end before he gets to fight, leading to a non-fatal massacre of both sides just to get back at her ex who dumped her. It is believed that she is asleep within the true Karakura Town in its temporary location in Rukongai. It should also be noted that Mizuho possesses an exceedingly violent and bossy nature, as seen by the way she reacts to even the slightest of comments as well as the treatment of her brother Keigo.

Filler
In the filler, Ikkaku and Yumichika stay at her place again while they are hunting an escaped experiment. During the time, she demonstrates that she's willing to throw him out for having hair. However, both characters experience development as she learns to overlook this when he saves her, and he looks on her more kindly.

Trivia

 * Mizuho closely resembles Wolfgangina Lalla Getto, the lead female character in another manga done by Tite Kubo called Zombie Powder.

Her treatment of Keigo is similar to Kukaku's treatment of Ganju, (and anyone else).