Mashiro Blan de Windbloom is the princess (and later Queen) of Windbloom. Her personality is completely opposite to her Mai-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 Mai-Hime what her true age was but in Mai-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 grow closer. It was at this point that Mashiro's personality began its gradual transformation. When the prince of Zipang came to visit Windbloom, Mashiro escaped the palace and met Takumi, the true prince of Zipang in disguise as a civilian. Takumi showed Mashiro the realities of her own city and she was appalled by the poverty that plagued Windbloom. Her encounter with Takumi caused Mashiro to feel great shame, thinking herself to be a useless queen. She withdrew to her room and sulked in solitude for days. On Chie's advice, Aoi brought Arika to talk with her. The two girls discussed their feelings and uncertainties, resulting in the both of them breaking down into emotional tears. Once calmed, the two made a pact that they would be "racing" to see who could achieve her dream first: Would Arika become a Meister Otome first, or would Mashiro become a queen who could bring happiness to her country first? Mashiro declared herself to be "reborn".
After Mashiro had delivered a speech to the people about her reborn self and the rebuilt castle that symbolized it, the castle's unveiling revealed that Schwarz had taken control of the castle and built a cannon on top, with which they began an attack on Windbloom. It was later revealed that Mashiro was blamed for this act even though she had no knowledge of it.After the fight between Nina and Arika, Mashiro took flight from Windbloom with the homeless people she had encountered during her meeting with Takumi, including a young orphan named Mimi. After wittnessing Aoi's self-sacrifice in order to keep the queen's whereabouts a secret from an angry mob, Mashiro was stricken with grief and shame at her own cowardice and failure as a ruler. She fled alone into the desert, and collapsed.
She awoke in the Aswald village, where she was reunited with Arika. Mashiro gained an intense admiration for Midori, the Aswald's boss, for her cool competence as a leader, and aspired to be like her. After wittnessing the death of another innocent that she could have saved - this time the young Mimi - Mashiro came to a personal epiphany She both aplogized and swore to the few gathered Windbloom refugees that she would completely reform herself and perform as a true ruler should, if they would give her the chance. She also promised Midori that she would share Garderobe's technology with the Aswald people as repayment for giving shelter to the Windboom refugees. She and Arika came to a full acceptance of their contract and swore loyalty to each other.
When she was brought to the Black Valley, upon Natsuki's advice Mashiro asked Mai Tokiha, Takumi's older sister, to help her train her to be a better queen. To Mashiro's chagrin, Miyu, who displayed a wealth of knowledge on the history of Arika and Windbloom itself, did not know where Mashiro came from or anything about her true past. Miyu does hint that Mashiro may be a descendant of Fumi, the original Otome and current Shinso. In any case, it is highly possible that Mashiro is of Royal Blood, depicted in episode 7, she was able to play the Harmoneal organ probably as the role of conductor. During the final battle, Mashiro gave full support to Arika and truly revealed herself to be a changed individual. Her leg was broken, and she was restricted to a wheelchair until her Coronation. In the end, she finally becomes Queen of Windbloom and keeps her promise to both Midori and the poor people of Windbloom.
Mashiro has made three contracts. In the main series, she makes one interim contract with Nina Wáng and a permanent contract with Arika Yumemiya. She makes a second interim contract with Nina in My-Otome Zwei.
During episode 1, a SLAVE attacked Mashiro and on Nina's advice, she acted as an interim master to allow Nina to fight in her Coral robe. In episode 7, Mashiro, accompanied by Arika, accidentally sounds Harmonium, shattering both of their Coral GEMs. A SLAVE then comes after the two of them. The Blue Sky Sapphire protects the two by blasting the SLAVE. With the SLAVE temporarily out of action, the pendant released its two GEMs so Mashiro and Arika could make a contract. With the Sapphire robe, Arika easily defeats the SLAVE. However, when Arika is injured in the fight, she sees Mashiro injured as well and remembers Natsuki's words; once a contract is made, an Otome will be sharing her life with her master. If she falls, so does her master and vice versa. In Mai-Otome Zwei episode 4, Nina approaches her with the Neptune Emerald GEM requesting an interim contract, which Mashiro obliges. Arika and Nina then work together to destroy Yuna. After Arika and Mashiro forge their contract with the Blue Sky Sapphire, they remove their GEMs (to avoid suspicion). Eventually Miss Maria discovers that Arika has "lost" her Coral GEM and has it replaced (and both of them punished severely).