The recently released collection Koin Illustrations contains art work from the light novels Haiyore! Nyaruko-san, Metal Witch Sisters, and Hauhau. Though Koin is probably best known as the illustrator for the popular series Kanokon, art from that series isn't included as there's already been an art book dedicated to it called Foxmark Kanokon Art Works.
Koin Illustrations is an A4-sized art book and 128 pages. Haiyore! Nyaruko-san takes up the majority of the book, with the first 47 pages of the collection. Most of the illustrations are fit to a full page, and the ones that aren't are generally two-page spreads. The series has great art work, mostly featuring the lead character, Nyaruko and less frequently the fiery Coo-ko.
Immediately following Haiyore! Nyaruko-san are the illustrations from Metal Witch Sisters, which have an older Koin style that feels a lot more painted. I'm not at all familiar with Metal Witch Sisters but it takes up the next 20-pages of the book, with loads of flowers, school uniforms, and thigh highs.
The last series featured is Hauhau, but only for 6 pages. The last few color illustrations are from GA Graphic wallpapers, though there is one tribute illustration for Shinkyoku Soukai Polyphonica. Color art works end at this point, and the last 40 pages are all monochrome.
The monochrome section features the inner novel art works from all of the above series, and in that same order. Some of the monochrome works are given a full page, but most are tiled four to a page in a slightly overlapping format. The last 10-pages are rough sketches of some of the colored works.
I really thought that Koin Illustrations was going to include way more of his original art works, and I was disappointed that it did not. Added to that, it's only really 78-pages of color illustrations for ￥2500. For a dedicated fan of the artist or the series, it would probably be worthwhile, otherwise, there are better art books out there for the price ^^;