First, "neko" means cat in Japanese. Then there's "p" which might stand for "pure" or part of a term like "Neko-P". "Shounen ga otona ni natta natsu" translates to "The coming of age summer of a boy". The "01" suggests the first part of a series.
In the age of information overload, we occasionally stumble across strings of text that defy immediate understanding. One such example is the keyword: nekopoishounengaotonaninattanatsu01