This 3-episode OVA based on the manga of the same name centers on twin sisters Ruka and Rumi who both have a crush on the same guy named Katsuyuki. The twins get infected with a mysterious substance from an old burial site that imbues them with powerful psychic abilities whose strength seems to be tied to moon cycles. The infection also causes Rumi to undergo a dramatic personality change, and she becomes ruthless in attempts to kill Ruka so she can have Katsuyuki for herself. Meanwhile, Katsuyuki has confessed his love for Ruka, and is adamant that he wants to be with her and not Rumi. As Rumi infects just about everyone around them and turns them in to virtual zombies bent on capturing Katsuyuki and killing Ruka, can the two protagonists escape her wrath?
The beginning of the OVA is promising, but the plot starts to derail quickly as it rides on the protagonists making mind-bogglingly stupid decisions to progress. For instance, after Ruka finds out that her sister killed a classmate, and her sister just attempted to murder her, she acts like it’s a minor inconvenience. She keeps going to school (that her sister also attends) and living at home (where her sister also lives) like everything’s normal. And her would-be boyfriend encourages her to do this. This kind of thing happens repeatedly, to predictable results. They also try to bring Rumi to the doctor so the sisters can be examined, and the doctor proclaims that they’re infected with a bacteria “that may be a virus.” In addition, there’s talk comparing what happened to them to Tutankhamen’s curse, etc. There are inconsistencies in the writing at some points as well.
As this OVA is basically made for fans of the manga, it’s incomplete, and ends abruptly. There’s no conclusion, and the characters are barely developed, if at all.
Speaking of the characters, Ruka doesn’t have much of a personality; she’s just super gullible and weak. Rumi’s personality is essentially that she’s evil and jealous of her sister. Katsuyuki is really pushy in is insistence on pursuing a relationship with Ruka, to the point that he forces himself on her a couple of times. All other characters are one-dimensional, if even that.
As far as technical aspects go, the animation is serviceable, but it’s not that good. The character designs are okay, but not distinctive; they look like the kind of designs you'd find in any other shoujo work. There are some good voice actors in this OVA, but their performances are just average. The ending is just a slideshow of manga images set to a cheap-sounding instrumental track that doesn’t really fit the series. The opening is another generic instrumental piece, and the background music is bland.
Regarding objectionable content, there are several graphic and bloody murders, and a couple of attempted rape scenes. There’s also a little bit of stylized nudity during the opening sequence.
Overall, in addition to poor technical aspects, “Umi no Yami, Tsuki no Kage” is filled with lots of dumb decisions, bad dialogue, inconsistent writing, characters not acting realistically, and an abrupt ending. While the premise is promising, it’s explored poorly here, and there are anime that do what this OVA was trying to do much better (see the recommendations). I wouldn’t recommend watching this unless you’re absolutely starved for shoujo horror content, or you’re a fan of the original manga.
