lightl beat me to it.
It's much like EnA's Special Edition, Seinarukana's Special Edition is a port of the ported console version, which is an improved (35 new CGs, improved scenario, and new recording) port to the original, but retains the ero/explicit contexts and scenes. Included in this edition are: Seinarukana's fandisc, the Seirei Tenshou (prequel) and its fandisc, and EnA Eternal Sky with possible CG and in ADV (I think?) format.