If you've been watching anime for a little while, I think that specials are usually nothing more than short funny fan service episodes. That's exactly what you get here. There's a beach trip, some private training for Issei, pervy Koneko, the first dress break, and more. I found them to be really funny. High school DxD isn't exactly a show that needed special comic ecchi relief though. It worthwhile to take the 22 minutes and watch them. Overall, they're a good source of entertainment. These episodes do not add any plot elements so if you're looking for
that, stay away.
Look, this is about as close as you can get to hentai without male/female sexual contact... oh wait, I do believe that this happens in these specials. This is like the fanservice for a fanserve kicked up a few degrees, because as far as writing a story goes for a 5 min special the old saying is "when in doubt, find some tits, and whip 'em out"... oh thats not an old saying, just me... I enjoyed them though so if you like the show, spend a half hour watching this, theyre fun.