Mira was captured by the KGB through Amalgam influence and subjected to extensive testing for Whispered capability at a special facility in Siberia. The testing involved the heavy use of drugs and psychological methods, which took a heavy toll on her mental state. Chewing her fingernails past the quick became the only way she could generate any sense of feeling.
A Mithril intelligence agent sent to infiltrate and investigate the facility saw her condition and abandoned his original mission in an attempt rescue her. He managed to get both her and a disk containing Whispered information out of the facility before the vehicle they were travelling in was destroyed by a pursuing attack helicopter, killing the agent and throwing her clear of the wreckage.
Before she could be recaptured by the KGB, a Mithril Special Response Team was able to complete her rescue using a trio of M9's inserted under the cover of ECS, with Sousuke using his AS to engage and destroy the helicopter.
Mithril then assisted her recovery from the KGB testing program in secret. By her own admission, the trauma of the testing never fully left her, however she was able to contribute to the Mithril's R&D division.
After the battle at Jindai High School, she was able to implement the ARX-7's Lambda Driver and Artificial Intelligence "Al" that were salvaged by Wraith into a new Arm Slave design known as the ARX-8 Laevatein at a secret location in Alaska, alongside Wraith and Gavin Hunter. The new AS design, notably its armament, was predominantly crafted by Mira in collaboration with the AI system to suit Sousuke's combat style.
She also applies the finishing touches to the development of Kaname Chidori's Fairy's Feather, a Black Technology device that cancels-out Lambda Drivers, prior to its fitment to the ARX-8 before the battle at Yamsk-11.
It is also shown that she is an acquaintance of fellow Whispered, Nami.
Later, she is relocated by Hunter to a secret safehouse where she, presumably, lives out a normal life in peace and calm, regularly maintaining contact with Sousuke via email. For all that he did for her, she has feelings for him although she recognises it would make things worse for Teletha Testarossa and Kaname Chidori, so she puts them aside.
"You are the one I owe my life to, and thus my heart is yours (though if you asked me to, I would do anything, but then Teresa-san or Chidori-san would probably kill me, so I will abstain)."
Before his final battle she sends him a memory card via Michel Lemon, that has a copy of a video his classmates uploaded wishing him and Kaname a safe return to school.
As a Whispered, she is aware of Leonard Testarossa's final plans for the world, and Tessa's opposition to it. While more partial to Leonard's ideology, she is happy to spectate and let things play out.
Kudan Mira is regularly called "Sarah Miller" in several English translations of the original novels. This is likely due to her English surname "Miller" being broken down into the Katakana spelling "Mi-Ra" (ミーラ) and getting lost in translation.