In My Otome, Mashiro Blan de Windbloom is the princess (and later Queen) of Windbloom. Her personality is completely opposite to her My-HiME incarnation. Rather than the polite, selfless and reserved attitude of the former, Mashiro Blan de Windbloom is boisterous, selfish, and arrogant. There are doubts on whether she is the true ruler - doubts which prove correct when the true ruler of Windbloom is discovered by Sergay Wáng. Mikoto the cat is her pet. She has a love-hate relationship with Nagi, leaning more towards the 'hate' end of the spectrum. It was never made clear in My-Hime what her true age was but in My-Otome it is explicitly said that she is 14-years-old and later turns 15.

She first met Nina and Arika when she was evading her palace guards by attempting to jump to the next building's roof. When she fell the two rushed to her aid. Believing the guards to be kidnappers, they then helped her escape. Arika, who was raised in the country, was completely clueless as to Mashiro's arrogant attitude toward her, even when she showed them that she was the princess in which Nina apologized for their ignorance.

As time passed, Mashiro pushed the people around her harder and harder. She would repeatedly shirk her responsibilities as queen in order to visit Garderobe and laugh at Arika's clumsy attempts at Otome training. When the date of her birthday drew near, she increased the taxes to raise more money for the rebuilding of her castle and her own birthday celebration. As Sergay Wáng noted, the city was suffering from increasing unemployment. Small glimpses of her past revealed that when Mashiro was young, she was completely spoiled as a child, being given virtually anything she wanted on demand. When she overheard some of the rumors that she was not the true princess, Mashiro's behavior worsened due to her highly increased feelings of insecurity and inadequacy.

During an emergency, she formed a contract with Arika to save their lives. Unfortunately for the two, the search for ways to break the contract yielded no answers. While Mashiro and Arika were initially very opposed to their contract, its life-binding conditions actually created a break in the tension between them, and they slowly began to