This Japanese art book for Assassin's Creed actually covers the first two games. There are only 120 pages here. Considering the amount of artistry involved, each game deserves its own book. Indeed, the first game had an art book but is already out of print.
The section for the first game has only 54 pages, compared to the 160-page English art book. You'll still get to see Altair designs and the beautiful middle eastern inspired backgrounds. But most designs for miscellaneous characters are missing. Even for those included, the resolution for some look a bit pixelated. All the art relating to Desmond Miles has been taken out. This section definitely felt lacking terms of character design.
For the second game, it's better in the sense that there wasn't any previously existing art book. Included are designs for Eizo, the weapons, backgrounds of 15th-century Italy and character designs for friends and enemies. Some of the art are also in the Collector's Edition game guide.
The art is very beautiful but the reproduction is, for the lack of a better word, questionable. It applies only to the first game. A cool gray tone is used as compared to the English book which uses neutral gray. It affects the character art and noticeably environments which look warmer and dryer.
Right at the back is an interview with Marcello Simonetta, an expect in Renaissance Studies. Text is in Japanese only.
A good bonus comes in an accompanying region code 2 DVD which includes the making of two games plus the live action scenes for the first game. The audio is in English with Japanese subtitles. The videos are very interesting and shows how the game was made, especially when they show videos of footage shot in Italy with the ones made in the game.
This is a book that will leave you wanting more, because there is more. It's unfortunate there's no dedicated art book for the second game.
Assassin's Creed Limited Edition Art Book is on the left.
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Here's the Amazon Japan buying guide for your reference.