Make a harem series that is roughly equal parts action, comedy, drama, and horror and you have this 10-episode, seinen manga-based Winter 2015 series (at least initially, anyway, as the horror element that is very prominent early on gradually fades in favor of the other three elements). Ignore the harem aspect of it and it is essentially a cross between Shakugan no Shana and Kekkaishi; Sakuya may use a bow instead of a sword or spiritual barriers, but the petite tsundere nature of the female lead, the family tradition of confronting supernatural creatures, the boy with a hidden power who helps the girl, that all carries over. And while Sakuya's seiyuu Ibuki Kido is only 17, her performance here is very reminiscent of Rie Kugimiya's rendition of Shana (or perhaps even more accurately, Taiga from Toradora!). In fact, it's so similar that the casting and/or directing choices have to have been done deliberately with that effect in mind.

Isuca differs markedly from those series by adding the harem element in and juicing up the fan service a lot. Its original broadcast/stream is heavily-censored, and not (always) without good reason, as screen shots from the initial Japanese BD release indicate that it does, indeed, contain detailed nudity. The series wastes no time getting to that, either; the first set of bared breasts is on the screen within the first minute, and more is to come before the first episode is out. Considerable more standard fan service fare abounds throughout the series, including panty shots even in places where it isn't really appropriate, clothes destroyed in battle, and having intense pleasure be a side effect of youma draining the life force from a victim. In fact, whether it or The Testament of Sister New Devil wins out as the premiere fan service title of their season is a close call; Isuca has more of it and generally better artistry, but Testament has the edge in intensity. Like its rival, it doesn't even let its theme songs pass without service, as the closer (which features an angelic versions of Sakuya and busty monster-catgirl Tamako in various sexy, unclothed poses) is also slightly censored.

If looked at first and foremost as a harem series then Isuca is just a little unusual in structure. While Shinichiro is the central male character for a harem which eventually included three romantic interests and five female characters total, he actually is not the series' central character; that, instead, is Sakuya. It is also a little more ambitious plot-wise than one would normally expect from a harem series, as very little of the content is true stand-alone shenanigans. Instead it has two main plot threads running throughout, ones which may, in certain aspects, be related. On the one side, Sakuya is maintaining her claim to be her grandmother's successor as head of the family mostly through sheer willpower, as her ascendancy is actively opposed by some who favor her cousin (and future fellow harem member) Suseri instead. The conflict all traces back to disapproval over her mother marrying a Western mage and some incident a few years earlier – which no one will explain in detail to Sakuya – which resulted in both her father and mother going missing. On the other side is the female mage who periodically either sends minions at Shinichi, Sakuya, and crew or else attacks them directly using Western magic. Exactly why she hates the Shimazu so much is never fully clarified, though it is implied to have something to do with a mysterious masked mage that she calls Father – and that mysterious mage is, of course, heavily implied to be Sakuya's actual father. There's actually some story potential on both sides, but unfortunately the series is too short to fully carry out either one.

Unfortunately, worthy plot elements and some mildly interesting character interactions do not alone make for a good series. No, execution definitely matters, too, and that is where the series stumbles the most. The problems are especially evident in the battle scenes, which are poorly-paced. Though not quite as egregious as Trinity Seven was on this point, too many characters (especially Shinichiro and Sakuya) spend too much time having involved conversations in the midst of a fight while the enemies just patiently wait around. (Either the original manga-ka does not have a good sense of combat timing or director Akira Iwanaga did not adjust enough for the different timing between manga and anime battle scenes.) The series also pushes too hard to work certain kinds of fan service in – I almost get the sense that Iwanaga had a bullet-pointed list of fan service tropes that had to be included – and too often fails to consider whether or not they are appropriate for the mood of the scene. The enemy mage's shtick also gets dully repetitive after a while; really, we get the point that you hate the Shimazu and want to do cruel things to Sakuya, so you don't need to remind the audience every 30 seconds. (This may be hyperbole, but not by too much.) Finally, Sakuya shows very little cleverness or variability in her fighting style; she seems to follow the philosophy of “if it does not work once in a fight, keep trying it and maybe it eventually will.” All of the other characters who regularly participate in the fights at least occasionally try something different.

The technical merits are not a problem, though. The animation, while far from top-rate, is good enough and has little trouble staying on model. Character designs show nothing innovative but are generally appealing, though the enemy female mage so perpetually has either hateful expressions or evil grins on her face that I must wonder if concept art featuring her with any other expressions even exists. Monster designs are nothing special, either, but the fan service (what we can see of it) is done well. Certain episodes also get quite graphic, though this does not end up being as common a feature as what the first couple of episodes suggest that it will be. Musical support is very efficient and effective, and both the opening and closing themes, while anime-typical in sound, fit well and are appreciable.

In other words, nothing about Isuca really does anything boldly different or special. It shows some promise but neither completely fails at it nor fully achieves it, as its strong points are enough to compensate for its flaws, but only just. Though it does finish at a proper stopping point, a second season will definitely be necessary for it to have a complete feel, especially given the surprise tidbit shown at the end. As of the time of this writing, word has yet to arrive on whether or not that will happen.