Hero Analysis for the Future

Hero Analysis for the Future (将来の為のヒーロー分析) is a set of notebooks belonging to Izuku Midoriya, thirteen of them in total.

Overview
Izuku uses these notebooks to jot down his own analysis of Heroes (including the students of Class 1-A) and their Quirks after observing them in action.

The contents of the books are apparently very detailed and well-written, to the point of impressing even All Might after he took a brief look at the pages of one of them.

Izuku also uses this book to write down ideas for his own hero career, such as Costume designs, combat strategies, and potential Super Moves. Izuku treasures these notebook, as they contains years' worth of observations about numorous Heroes that he admires.

At the beginning of the series, Katsuki Bakugo had stolen, burned, and then tossed the 13th notebook away in front of Izuku, who had managed to retrieve it later. All Might also signed an autograph in this notebook after saving Izuku from the Sludge Villain.

During his mock battle with Katsuki, Izuku is revealed to have memorized the contents of the books, which he told Katsuki, who recalled the book and was angry that the once weakling had an edge over him.

At the Sports Festival, it is revealed Izuku has documented the Quirks of all his classmates. A majority were shocked at the extreme detail he accumulated and rejected any help from the notes in their match.

Trivia

 * Izuku's current notebook is from the Kokuyo Campus Note notebook brand (changed to "Campos" and "Kukuyo" in the main series)
 * Izuku has, or at least had, multiple notebooks, as the one used at the start of the series had a numerical identification (in this case, "No. 13"). Brief images of notebooks 1-12 and their covers can be seen in the opening sequence for THE DAY, and Episode 13.5.