* AlternateCharacterInterpretation
** Zorndyke. Dear lord Zorndyke.
** Hayami and Mutio, and whether their [[InterspeciesRomance romantic relationship]] was one-sided. Mutio is clearly smitten with Hayami, but Hayami didn't seem to return these feelings, beyond simply being concerned for her safety.
* BigLippedAlligatorMoment: The seemingly PerfectPacifistPeople introduced towards the end given how they pop up during a war of genocide.
** The scene in episode 2 where Verg [[LecherousLicking starts licking]] one of Mutio's sisters during his VillainousBreakdown, and then Mutio herself when he finds out that she made physical contact with a human during the battle. Both are done in a [[{{Squick}} very disturbing]] way.
** During the scene in episode 1 where Hayami saves Mutio and brings her into the water, Mutio stares at Hayami before emitting a sonic cry of some sort. Why she does this is not explained, and we never see her nor any of her sisters do this in the rest of the OVA.
* CultClassic
* CrowningMusicOfAwesome: ''The entire soundtrack'', performed by (unknown outside of Japan) funk/jazz group The Thrill. Released on CD in Japan.
* EnsembleDarkhorse: Mutio, for her unique design, passive nature, and relationship with Hayami.
* HarsherInHindsight: Seeing the city of Tokyo, flooded and in ruins, can seem unsettling after the earthquake and tsunami that hit Japan in 2011.
* HilariousInHindsight
** Hayami asking Kino if he can smoke while they're repairing Blue 6 can be this to American viewers, given that the U.S. Navy banned smoking on submarines in 2010.
* ItsShortSoItSucks[=/=]TooGoodToLast: A common critique of the show is that while it has an interesting premise, characters and lots of potential for both of those to be developed the fact that it was only four episodes long kind of made that impossible.
* {{Moe}}[=/=]TheWoobie: [[CuteMonsterGirl Mutio]].
* TheScrappy: Kino, who gets a lot of flak due to her constant whining and arguing with Hayami.
* SuspiciouslySimilarSong: The music that plays when Verg arrives to mourn Zorndyke's death, known on the soundtrack as "Mina Wa ni Kaere", sounds very much like "Imagine" by John Lennon.