The second season of Knights of Sidonia picks up almost exactly where the first season left off, with no recap whatsoever. Hence at least reviewing the events of the first season before beginning this one is strongly recommended, or else the first episode will be a confusing mess.

Effectively, the second season involves three main plotlines which each occasionally but not consistently intersect with one or both of the others. One involves the gradually growing relationship between Nagate and Izana, which triggers her growth of more specifically feminine characteristics; look for her bust line to change radically by the end of the series, as well as other subtle and not-so-subtle character design modifications. (Sadly, the full implications of this change, which is arguably the series' most intriguing and distinctive development, are not explored.) Tsumugi also soon gets added to this mix in a progression of events which can only be described as rather warped and a hair's breadth from being totally creepy, and eventually Yuhata gets involved, too. In fact, before the series' end Nagate pretty much has a harem developing, as Ren is also far out on the periphery and at least one or two other female characters seem to have taken a shine to him, too. That also means that some of the comedy elements in the middle episodes provide a harem romantic comedy flavor.

The second plot line involves what Kobayashi and Ochiai, who seem to be in cahoots, are working on behind the scenes. Sometimes their efforts bear fruit (Tsumugi), while other times they bear disaster (the Gravity Beam Emitter). This line largely gets ignored in the later stages of the series, but by then the series clearly shows why Ochiai got in hot water in the first place: his sense of risk assessment is rather poor. The third plot line, which dominates the last quarter but is present throughout, focuses on the confrontations with the Gauna, who are evolving in nature and tactics to combat Sidonian forces, who are also regularly coming up with their own new equipment. Essentially the Gauna-Sidonia conflict is becoming a classic shonen battle of one-upmanship.

Nothing about the way that the third plot line plays out is all that innovative, but that does not prevent the series from generating some incredibly intense battle situations and action sequences. At their very best these sequences become glorious affairs, such as the climax of the battle on Planet Nine in episode 12, which ranks amongst the best mecha battles of recent years despite lacking much for individual heroics. In fact, it serves as practically the ideal for what mecha units acting in militarily-precise unison can do. Of course, that does not mean that there aren't a lot of individual heroics and show-off moments in other scenes, but in this season Nagate is not the only one getting those scenes. Tsumugi at least matches him in that regard, and even Izana has a couple of moments herself.

The visuals by Polygon Pictures maintain the quality level seen in the first season, for better or worse. (In other words, if the nature of the CG animation turned you off in the first season, nothing that the second season does will change that reaction.) The artistry still emphasizes wear patterns on just about everything and the bust lines of some of its female characters, though its actual amount of fan service is limited to just a handful of scenes across twelve episodes. It still produces some fantastic designs on equipment, scenic vistas, screen displays, and architecture (Nagate and Izana's new home in particular is neat) and the animation tends to be much smoother in action sequences than in character animation. Remarkably, it manages to turn Tsumugi's use of pseudopods from something which should be very disturbing into something actually cute. The drab color scheme does wear on the eyes after a while, but that also makes the rare scene which does use more vibrant color all the sharper.

The soundtrack continues in the same style as the first season: heavy electronica mixed with dramatic vocals and symphonic numbers reminiscent of military marches for the most part, although it does have a few lighter tunes for the more light-hearted moments, too. It still comes on a little too heavy at times, but it also still faithfully juices the intensity of the action scenes. The used of sound effects in this season also stands out, particularly in a late confrontation with the Crimson Hawk Moth – yes, it does show up again. Fantastic original opener “Sidonia” is instead used here as both an insert song and (in extended form) as the closer for the final episode. Replacing it as the regular opener is the new “Knight March,” also by angela, which has the same style and feel, the same approach of mixing an electronica dance beat with military marches, but is also a step down in quality. New closer “Requiem” is less memorable or distinctive.

The Netflix stream of the series has Japanese, English, and Spanish dubs and subtitles for the latter two available. The entire English cast continues from the first season, with the only “new” role, that of Tsumugi, also being done by Alexi Shi (who is either Stephanie Sheh under a pseudonym or a vocal dead ringer for her), the voice of Shizuka Hoshijiro; both roles are also done by the same voice actress in Japanese. As with the first season, the occasional problems of awkward pauses and slightly stilted delivery continues, likely a result of trouble with getting the dialog to time right with the lip flaps. This is an infrequent problem but happens virtually across the board, with the only voice actors completely avoiding it being those whose characters never have visible lip flaps, which suggests a problem either with the direction or with a script that stays too tight or both. Either way it is not a big distraction but still a definite flaw.

The end of this season evokes a sense of closure for Nagate, which seems tacked on because he never really gave the sense that he was striving for it. The end also tries to give a “the adventures continue” feel, though it leaves far too many major plot threads floating for it to really have any proper resolution or sense of movement forward. Basically, the story just ends, stopping at a point that is more mid-season break than conclusion. Spoilers for the source manga suggest that there may be enough more to animate at this point to justify most or all of a third season, but about that we'll have to wait and see. As is, it still serves reasonably well as a dedicated, if not terribly original, mecha action show.