Mikoto Minagi plays an important role in Mai's story, while she has her own plot as well. She is a third-grade middle school student in the same class as Nao Yuuki. She loves to be with Mai, often at her side or clinging to her. She also has a problem with spicy food, and consuming it often sends her into rampages while looking for water. Mikoto is usually seen with her two-handed sword, Miroku, either in hand or in a black sword bag.
Mikoto first appears in episode 1 as a nearly drowned girl rescued by a passing ferry and resuscitated by Mai. She fights off Natsuki Kuga, eventually cutting the ship in half and causing Mai to rescue her again. Mikoto reappears in episode 2, taken in by Mai. Mikoto tells Mai her purpose for coming to Fuka Academy is to look for her older brother.
During the next episodes, Mikoto aids Mai and Natsuki Kuga in battling the Orphans that appear while also continuing to search for her brother. Mikoto's main conflict is first hinted at in episode 12, when she realizes that she likes Mai, conflicting with her love for her missing brother. During a flashback it becomes apparent that she killed her grandfather as part of a test before she left for Fuka, for which he commended her. In episode 18, Mikoto's pendant glows for the first time, and her brother's command to defeat enemies is revealed in a flashback. Mikoto becomes torn between defeating enemies and protecting Mai, or obeying Mai's order to not fight the other HiME.
Under the command of her brother (revealed to be Reito Kanzaki, the Obsidian Lord), Mikoto protects Mai and fights the other HiMEs, resulting in the defeat of Akira Okuzaki, Midori Sugiura, and Shiho Munakata. The deaths of Takumi Tokiha and Yuuichi Tate resulting from the HiMEs' defeats drive Mai into depression, subsequently causing unhappiness for Mikoto.
In episode 26, Mai and Mikoto finally face each other in battle. Their battle ends when Mai openly states her love for Mikoto, breaking the Obsidian Lord's control over her. Mikoto breaks the pendant around her brother's neck, also freeing him from the Obsidian Lord's control.
Element and ChildMikoto's Element is Miroku, a black two-handed sword resembling a claymore. She is able to strike with great force and has cleaved a ship in half. She is also able to summon Miroku when physically separated from the sword. Her HiME mark is on her upper right arm.
Mikoto's Child is also named Miroku, and is a large giant with an equally large spiked club. It is first fully shown on screen in episode 23, though it does appear in earlier episodes causing spikes to come out of the ground at Mikoto's command. Mikoto herself does not appear to completely control the Child, who is referred to as the protector of the Obsidian Lord and attempts to block an attack against him during the final battle.
In the manga, Mikoto wields Miroku and is capable is using an attack that can split the ground. Mai states that Mikoto is the strongest of the HiMEs and can defeat the other HiMEs' Childs. Mikoto's Child and Key are not revealed; in fact, Mikoto herself states in chapter 11 that she doesn't have or need a Key, although this might just be boasting on her part.