ユーリ・エーベルヴァイン
Yuri in [[Mahou Shoujo Lyrical Nanoha A's Portable: The Gears of Destiny|The Gears of Destiny]], although Unbreakable Dark has been mentioned by the Materials in [[Mahou Shoujo Lyrical Nanoha A's Portable: The Battle of Aces|The Battle of Aces]].

Born in the Ancient Belkan ages, Yuri was originally a single entity. However, due to a program written with the aim of overwriting the Book of the Night Sky, Yuri was turned into Unbreakable Dark (砕け得ぬ闇 Kudake'enu Yami), aka System "Unbreakable Dark" (アンブレイカブル・ダーク Anbureikaburu Dāku) or U-D (Ｕ－Ｄ Yū Dī) and divided into multiple entities.

She is according to herself and the Materials: The True Darkness of the Book of Darkness and her Examia energies are responsible for the rampages of the Book of Darkness's Defense Program (the Materials themselves) that destroy worlds.

So uncontrollable are her powers that she and her Book of the Purple Sky were transferred into the Book of the Night Sky(which at the time was a Storage Device) causing parts of her program to segment into the Materials with Material-D which serves as the core of both the Defense Program and the Book of Darkness itself(outranking the Book's Master Control Program) segmenting further to create the Wolkenritter.

When battling Vivio Takamachi as U-D in 0066, she mistakes Vivio as the Heiliger Kaiser of the Cradle. From their conversation, it is also revealed that she knows Olivie Sägebrecht.

By the end of the Unbreakable Dark Incident, Yuri eventually has her Examia overwritten by Dearche(similar to how Hayate overwrote the Book of Darkness returning it to becoming the Book of the Night Sky) and is given back the name she had before splitting into U-D and the Materials.

Yuri in the movie continuity.

Near the end of Reflection, it is revealed by Iris (who calls Yuri a Demon) that she died during a disaster caused by Yuri decades ago, and now she is going to take revenge. When Yuri is unsealed/wakened from the Examia crystal, she is quickly mind-controlled by Iris with the virus codes before their conversion is finished, causing her to attack the Administrative Bureau mages including Fate T. Harlaown and Signum with Crystal Tree.

In Detonation, after Nanoha Takamachi comes to save the Administrative Bureau mages using Formula Cannon, Iris order Yuri to attack Nanoha. As Nanoha had activated System Alter, she is able to dodge Yuri's attack. The fight goes on until Nanoha's body gets injured due to the negative effect of System Alter which allows Yuri to land a finishing blow. Nanoha is then saved by Vita, Signum and Hayate. Soon, Iris order Yuri to leave the area.

Later, after Levi recovers one of Tome of the Night Sky's pages that Yuri wanted the others to have, a shared past from Yuri and Iris is shown. It is revealed that Iris first met Yuri in a small cave on Eltria 40 years ago. Yuri tries to speak with Iris while using Belka language but due to Iris not being able to understand, Yuri enables the Book of Darkness to activate the translation system so she can speak the same language as Iris. Yuri introduces herself as a guardian of the Book of Darkness; her duty is to watch over the tome to prevent NachtWal from going berserk and from killing its master. After their conversation, Yuri reveals an ability which leads the laboratory members to believe she is the key to revive Eltria, so they ask her to stay with them and Iris. The flashback is suddenly skipped to a scene in which Yuri seemingly killed Phil Maxwell and Iris. Yuri states they will meet again in the future. The Book of Darkness disappears alongside Yuri to another planet. It is also explained that the reason why Yuri didn't show up to stop NachtWal during the Book of Darkness incident was because the page that contained Yuri's guardian system got lost in the sea and transformed into a crystal after NachtWal was destroyed in space.

Soon, Iris orders Yuri to attack Tokyo along with the Iris Units. The three materials come to fight against Yuri. During the fight, the trio slowly regain their memories and remember that they were once cats who lived with Yuri and Iris. After the three materials take down Yuri, she breaks free from Iris' control. Suddenly, an android shows up and attacks the materials, severely injuring them. It's revealed that the android is Phil, the laboratory chief that was supposed killed by Yuri 40 years ago. Phil takes Yuri and flies toward the Tokyo Station. After receiving the mana energy from Stern and Levi, Dearche in Trinity Blood Form faces Yuri to save her from Phil's control. For a finishing move, Dearche begins to charge Excalibur Trinity. Yuri tells her to stop or she will transform back to her original cat form, but Dearche doesn't listen stating they wouldn't regret giving back all the love Yuri gave them back then. After successfuly casting the spell and transforming back to cat form, Yuri finally breaks free from Phil's control and embraces Dearche.

Near the end of Detonation, Yuri and the three materials go to Eltria along with the Florian sisters. While living together with the Florian family, Yuri and the others succesfully revive Eltria.

Yuri in [[Mahou Shoujo Lyrical Nanoha INNOCENT]].

Yuri Eberwein is an international student studying abroad in Uminari City.
yuri eberwein