Eibunkan is the first English grammar in Japan published in 1841, when Japan was still closed to the world. When he wrote it, Shibukawa was working for the Tokugawa Shogunate as a probationary computist.
Originally, only three copies were made; one was presented to the shogunate, another was given to the office of computus he was working at, and the other was kept by himself. The first two copies were lost and the only one extant was in possession of one of his descendants, Tamiko Shibukawa, who reprinted it in 1928. Only a hundred copies were made. It is not clear where the last survivor of the three original copies is preserved now.
Japan kept contact with the Netherlands even in the period of national isolation, and in those days, everything Western was learned through books in Dutch. This is why Eibunkan is based on a Dutch translation of the 26th edition of Lindley Murray's Grammar of English Language (1795), Engelsche Spraakkunst, first published in 1816. English words, phrases, and sentences are rephrased in Dutch and Japanese, while many of the exercises given at the end of each section or chapter are Dutch-English translation (as in the underlying Dutche version). Thus it is somewhat like Dutch-English comparative grammar for Japanese readers fluent in Dutch.
The Japanese word for the English language, eigo (英語), is used allegedly for the first time in this book. It is used only once in the introduction in pseudo-classical Chinese seemingly to mean 'English words' rather than the English language. So it may not really be the first example of the word used in Japanese in the sense in which we use it now.