Kosuke Fujishima's Ah! My Goddess Collection is the artbook - or rather an encyclopedia - celebrating the 15th anniversary of Oh My Goddess. It feels like the a treasure trove of Oh My Goddess information but has the small, but problematic flaw that non-Japanese speaking people can only guess what it is all about (unfortunately, it hasn't been translated yet.) However, some things can be said about it.
One note about telling that it is an artbook. Although it contains art from the manga, with its normal manga format and few colour pages it probably wouldn't qualify as an artbook in the usual meaning (most of the colour art that appears in it is from manga cover illustrations or from other Oh My Goddess products.) Its real strong side seems to be the reference information - with an extent unprecedent by any other Oh My Goddess publication.
The volume starts with a small foldout poster of the five goddesses as well as Hild, Megumi and Chihiro in swimsuits (a little note, nothing unseen, it's just a collage of the frequently displayed swimsuit illustrations, as Fujishima himself said in the manga artbook, "doesn't everyone like bikinis, this illustration [Belldandy in a bikini] has been printed so often, it became clear to me that 'really everyone likes swimsuits' ".) On the backside of it, there is a diagram called correlation map, that illustrates the relationships between the more important characters. It features the Morisato family, the five goddesses (as well as Lind's angels Coolmint and Spearmint), the demons Hild, Marller and Welsper, and also Chihiro. The love relationships indicated on it are Keiichi and Belldandy (ok, we knew that), Skuld and Sentaro and Banpei and Sigel (this one only in one direction - Banpei to Sigel - with a question mark in the other direction.)The forword is done as an interview with Kosuke Fujishima. "Digest", the first chapter, summarizes selected chapters of volumes 1 to 29. The next few chapters "Belldandy", "Urd" and "Skuld" seem to focus on the three goddesses and their specific talents and hobbies (all with some kind of reference to specific events and the chapters in which they occured.) Maybe now is a good point to mention that while not many romanic words appear, they help to clarify the intended translated spellings at the time of the publication of this book. The most discussed one probably is Lind (spelled exactly this way) with her angels Coolmint and Spearmint (without spaces.) Just for completeness, the book gives us Belldandy with Holy Bell, Urd and World of Elegance, Skuld and Noble Scarlet as well as Peorth and Gorgeous Rose. More interesting are Sentaro (rather than Sentarou) and Troubadour. On the demon side, we have Hild, Welsper (nothing special so far) and Marller (that one maybe is noteworthy.)