This is tough because I want to like Yuragi-sou no Yuuna-san. I started reading the manga earlier last year, I think, and I remember finding it, while not a materpiece, enjoyable enough. A light, ecchi story with a bit of heart and comedy. This OVA, or at least the first part released ahead of the anime itself, is a departure from what I believe made the series enjoyable (the comedy) and doubled down on ecchi.
The first episode covers two separate storylines. The first is a get-to-know-the-cast story, and the second is a bit from the manga. Both exist solely to show the viewer "dem anime tiddies." If that is all you want from this, then make hay; however, the barebone plot coupled with the poor animation quality (medium-distance scenes have the detail of long-distance in most other shows; there is not real detailing in the faces in close ups resulting in a very flat-feeling composition) make this OVA a turn-off to the series to the uninitiated. I know this series is better, but why would someone who has no contact with this series want to keep watching it based on this uninspired mess?
Maybe, though, I'm wrong and the manga is bad, too. To be fair, the manga I was reading was censored. So, everything happened behind "steam." I believe, in the complied releases of the manga, this was removed in favor of a more explicit rendering. Losing that varnish of mystique going from censored manga to this just leaves the series feeling crass and leaves a less familiarized viewer (with anime tropes writ large) feeling gross for watching it (the loli-in-appearance owner being visibly naked could be considered galling).
I must acknowledge that this is supposed to be a released-with-the-manga product, so it makes sense that it is light on everything except fanservice, but it doesn't function as a hat-tip to the faithful reader. It presents itself as an introduction piece to the full-length anime upcoming, and, on those merits, it fails. There is nothing enticing about this except for the fanservice, something I believe will be "steamier" in the broadcast show, so if you're on-board for that only, expect to be disappointed.
Perhaps I am being to harsh to what is ostensibly a little bonus piece of content, but it is so comically uninspired and so tactically being billeted right before the anime airs that harsh feels warranted. This is supposed to be the thing that gets you to tune in or buy the next thing. Instead, it is hapless predictable and woefully hollow. Just meeting this character? You're about to see her boobs. A lot. If you like that, give it a watch, though I'd recommend, if that is your goal, that you skip around and avoid having to watch the weak connective tissue pulling you from scene to scene.
Should My Sister Watch This Anime? No. I don't even want her to know I watched it.