The Unit Logbook is a unit database introduced in Fire Emblem Awakening.
The Unit Logbook is an in-game database that stores information of additional units obtained through various means, either by completing a playthrough or through StreetPass. In both of its appearances, it allows the player to buy additional units for their army.
The Unit Logbook allows the player to buy other Avatars as additional units in the army. The player receives the version of their Avatar that was used upon completing the Endgame, the Avatar of a StreetPass team upon defeat, or recruited by paying a fee. The price of the recruited Avatar depends on their rating, which is factored by their current Level, class tier, Stat spread, and equipped skills. Current equipped weapons are not included. Einherjar are also included in the Unit Logbook. The player can freely update their current save file's Avatar in the Logbook at anytime.
A maximum of 20 bonus units may be acquired, counting both Avatars and Einherjar units under this method and the Unit Logbook holds the data for 99 bonus units.
Fates expands upon Awakening's Unit, allowing the player to store all potential units in the Logbook, not just Avatars and Einherjar units. Players can acquire Unit cards either by completing StreetPass and Online battles, purchasing them through the Card Shop in the player's My Castle, and completing the Endgame of either route. For the last option, up to five members of the player's current army can be saved to the Unit Logbook each time an Endgame is completed. Additionally, these units stored using this method also retains ALL skills learned at that point and can be freely exchanged at any point. Fates units acquired via this method are treated as bonus units, and thus cannot form supports nor access their support bonuses from their original file.
Players may still buy copy versions of units in the book, with the price determined by the unit's current level, class tier, stat spread, and skills. Units acquired by completing the Endgame cost more than a normal Card Shop version of the same unit. Players may additionally purchase any equipped skills and all learned skills by Endgame acquired units. amiibo units, generic captured allies, and special captured bosses are also stored in the Unit Logbook. A maximum of 50 bonus units can be stored in this book and up to 20 may be present in the player's army.