This 13 episode series is based on a manga of the same name and aired during the Spring 2019 season. It is only coming out now because of the typical Netflix delay, but it does at least include Netflix's standard complement of multiple audio and subtitling options. Whether or not the series was worth the wait is a much more nebulous judgment call.

The basic premise has to be accepted at face value, as thinking at all about the actual consequences of a new continent nearly the size of North America suddenly appearing in the middle of the Pacific raises all kinds of questions that the series is completely unprepared to answer: things like where the displaced water went, what happened to the islands and people that were in that area (most notably the Hawaiian Islands), how the continent's appearance affects things like weather, currents, and earthquakes, and so forth. The series is also utterly uninterested in even contemplating things like where the continent came from, why it has flora and fauna so much more powerful than the rest of Earth, and how major world powers would react. It's a cool and dangerous place to explore, and that is all that really matters.

The setting isn't the only thing that exists without adequate explanation. How Inyo and Zero can operate out of the facilities they have, despite supposedly being so poor that keeping the power on or putting food on the table can sometimes be an issue, is never explained, and never mind the helicopter they use and seem to own, even if it is a basic one. Neither is where Lacht power comes from or how Inyo and Zero ended up with it – and considering that one or both use it every episode, this is a big omission. The writing is also inconsistent about how much of a secret being a Lachter is supposed to be; early on Inyo seems reluctant to show off the power to others, but later in the series he doesn't seem to have any qualms about it.

If all of the overhead baggage is ignored then what's left is a mostly standard shonen action-styled series, one which differs from its kin primarily by having a more environmentalist bent than normal. Two different episodes condemn animal cruelty as a focal point, with the one where it's done for (streaming video) entertainment value getting the harshest treatment. Another episode advocates against animal testing as a key plot point, yet another involves respecting indigenous populations, and not killing animals needlessly or wastefully is a recurring theme. The writing implies that it has no problem with killing animals for food or self-defense, so this is not an extremist position, and the theme is not pervasive, but it comes up too often to be coincidental.

The series' story structure lacks any overarching plot or goals, resulting in most of the content playing out episodically; not until the final three episodes, which delve into Zero's barely-hinted-at past, is the storytelling continuous. Despite that, several named characters who appear in earlier episodes reappear in one capacity or another in later ones, and one (the much-put-upon shopkeeper) even gets his own feature episode. Although the story mostly uses a serious tone, It occasionally find room for lighter-hearted content, whether it's Zero's make-over episode, the shopkeeper's failed attempts to win against Inyu's deviousness, or a whole run of jokes about marshmallows. Along the way the writing makes at least some effort towards character development, with Inyu getting more attention early and Zero getting more attention late in the series. Even so, characterization is not a strong suit. Inyu has three basic modes – light-hearted, businesslike, and Sharp Glare – but the only subtlety or shading to those modes is the sense of restrained anger he can give off when he's crossed. Zero, meanwhile, is likable but doesn't have much range to her until the final arc.

What the series might lack in characterization it mostly compensates for elsewhere, especially in its substantial action component. The static-like manifestation of Lacht is an interesting visual effect, one which Zero typically uses to create a bot-like drone she can operate remotely and which Inyu uses to create weapons, blocks to jump on, or giant hands. This rarely results in sustained action sequences, with only one fight in the first episode and another in the last being very involved. Even then, the quality of the fights does not stand out. They are interesting enough to watch but not memorable in either presentation or animation quality.

The visual technical merits of the series are most notable for their consistent quality control and the odd use of a grainy texture in many of the scenes set in Magmell, even ones that aren't flashbacks. Character designs are most distinctive for Inyu and Zero's eyes, which seem even a scale larger than normal and look a bit awkward in shots where they are seen from the side. Inyo also stands out for exclusively wearing an older-style military uniform, while Zero's signature accoutrement is a headset marked with the number 04 (whose significance is never explained), which she almost always wears even when not remotely speaking to Inyu through her bot. Monster design doesn't stand out, and settings are detailed but, again, nothing special. Despite Zero obsessing over one recurring female character's ample chest, that character's cleavage is the series' only fan service. Graphic violence is much more pronounced but not extreme.

The true standout element on the production front is the musical score. The rich and varied sound draws upon a wide range of instrumentation, including classical Chinese instruments like the ehru, to evoke a sense of mystique and intensity about Magmell. What tension the action scenes have is largely attributable to the efforts of Yasuharu Takanashi, whose other recent musical works include the likes of Zombie Land Saga and the Fairy Tail franchise. Opener “Dash&Daaash!” is more notable for its (literally) splashy use of color, but closer “The Key” is a memorable song by long-time recording artists a flood of circle.

The English dub is provided by SDI Media, the same studio group which produced dubs for Kabaneri of the Iron Fortress, Hi Score Girl, and Violet Evergarden. Though there are a few struggles with timing in the early going, the casting is appropriate and performances are otherwise competent. The one noteworthy effort here is Griffin Puatu's performance as Inyo, which takes a subtler but still effective approach at portraying Inyo's intensity. The English script varies some but not to a problematic degree.

Maybe the biggest plus about Ultramarine Magmell is that it tells an intact story. The ending leaves it wide open for further adventurers, but at least the series stops on a definitive breaking point, one that also wraps up its one significant plotline. Overall, the series could stand a lot more world-building, but if you're looking for an uncomplicated action-adventure series then it should fit the bill.