|Book of the Azure Sky|
|Other names||Buch der blauer Himmel|
|Master||Hayate Yagami (until 0069)|
|Magic system||Ancient Belka|
|Japanese name||蒼天の書 |
(Sōten no Sho)
|First app.||A's epilogue|
The Book of the Azure Sky (蒼天の書 Sōten no Sho, officially/Ger. Buch der blauer Himmel) is the Storage Device used by Reinforce II, similar to how her own master Hayate Yagami uses the Tome of the Night Sky.
Initially, the Book is shared by both Rein and Hayate. After Rein has passed the Administrative Bureau's employment examination in the autumn of 0069, it becomes necessary to increase data capacity. As a result, a division is needed and Hayate has then created her own Tome, letting Rein to use the Book of the Azure Sky exclusively.
The Book of the Azure Sky ("Buch der blauer Himmel") is named after the Tome of the Night Sky ("Buch der Nachthimmel").
Note that "Buch der blauer Himmel" is not proper German, since "Himmel" ("Sky") is masculine and the name should therefore be "Buch des blauen Himmels". Or, if "Himmel" is meant to be plural ("Skies"), "Buch der blauen Himmel".
About half of the data stored in it are the magic data for unison, Rein herself does not really use it for casting spells. Its role is comparable to an external hard disk drive. Though, it functions well in casting spells like Frierenfesseln, as well as in loading data for unison.