There are so many jokes I could make about this being another episode of Another, that I simply don't know which one to choose. Except I guess I just made that exact joke. Oh well.
As its name suggests, this OVA instalment acts as "episode zero" to the series, taking place before (and apologies for the spoiler) everything went batshit crazy and pretty much everybody died. In this happier, simpler time, we spend most of the first half of this episode watching the estranged Misaki twins enjoying one another's company, chattering and generally hanging out together. However, when the Misaki we know well sees an odd vision via her false eye, it suggests that something terrible is about to befall her sister.
With that knowledge floating around in her head, Misaki is determined to protect her sibling no matter what as they head off to a theme park the next day, protecting her from suspicious-looking people and fretting as they take to the park's rollercoaster. Just as it seems that there's nothing to worry about, the Ferris Wheel of all places threatens to be a violent end to their outing, only for any such worries to be dashed. There is, however, something even more dire waiting around the corner in the very near future for the fated Misaki...
Following what was practically a slice of life beginning to this episode (and a slightly fan service-laden one at that), this OVA clearly delighted in building up its anticipation of more bloody, violent death; playing that tension to breaking point before letting it drift away on breeze of false expectation. That clever play on the viewer's prior knowledge makes the final twist of the proverbial knife all the more shocking, and horrifying in a rather different way - it's something that the mainstay of Another managed to do only occasionally, but it was perhaps one of the strong points of a series that managed its creeping sense of horror rather well until it let the handbrake off during its second half. Still, this is a pretty solid OVA to round off the series and square its story-telling circle, so to my mind it makes for a decent addition to a half-decent anime.