The Secret Book (Japanese: 秘伝の書Secret Book) is one of several enhancing items in the Fire Emblem series. Its function is to permanently increases the skill of any unit by, usually, two points. Exceptions to this are the original Archanea games, where this item adds five points.
After receiving the data from the Mario Kart: Double Dash!! bonus discUS or from a Monthly Nintendo demo machine in June 2003JP, transfer it into a savefile through the Transfer Data menu. Only one can be transferred per save file, and the transfer can only be done from Chapter 12 onward.