My-HiME Manga
In the manga, much like in the anime, Mikoto wields Miroku and is capable in using an attack that can split the ground called Tosotsuken, a.k.a. Tusita Sword. 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. There is also mention of Mikoto having a brother, since Reito never appeared in the manga.
In a flashback, Mikoto didn't seem to trust anyone, and acted like an angry cat hissing at anyone who came near. Thanks to Mai, she started opening up. In one chapter, she took care of an OPRHAN with only Akira knowing of its existence. Mikoto said it was just like her back in the day. She was forced to destroy it when it awakened to its true nature.
Mikoto falls under the control of Shiho Munakata in chapter 30, forcing Mai to fight her. Later, Mikoto, Akira, and Nao Yuuki face off against Yang Guifei in chapter 39. The three and the QUEEN are absorbed by the HiME Star, but are freed when the HiME Star's Child is defeated.
Read more about this topic: Mikoto Minagi