The Eastern Princess, he is more reluctant than the other two Princesses to crossdress because he does not want his girlfriend Megumi to find out about it. As such he is nonetheless a reliable character - he often stubbornly whines and complains about things the Princesses have to do but always ends up doing them anyway whether he's forced to or not. He is very self-conscious about being a Princess and is mortified whenever someone else outside of school finds out about it. He is the most animated of the three Princesses, always showing a lot of emotion and expression when yelling at Toru and Yuujiro. Mikoto is also tone deaf, having never sung before becoming a princess.
He also cares a lot about the people close to him, though especially for his girlfriend. He has shown to change character and act different when around Megumi, which greatly amuses Toru and Yuujiro. Despite all the whining and complaining, however, he eventually becomes accustomed to his duty as a Princess such that he once had a brief fantasy of him and Megumi both dressed in Gothic Lolita Princess costumes. Princess Princess is not the first media series Mikoto has appeared in. Mikoto's first appearance was as a supporting character from one of Tsuda's earlier manga works, The Day of Revolution, which was about Mikoto's girlfriend, Megumi.
In addition, he is a jerk with heart of gold.