* AdaptationDisplacement: It's telling that the vast majority of the tropes listed are from the anime, which [[GeckoEnding diverges wildly]] from the manga, though not in a bad way.
* CrazyAwesome: The series in general.
* CrowningMusicOfAwesome: Lunarian, Your Gravitation, the Song of Heroes and the Song of War. There's also Setouchi no Ninkyodo, Gozaburo and Ren's image song, and Hageshii no Uta from the OVA.
* EarWorm: The OP. Watashi wa romantikku, anata mo romantikku....
** Good luck getting the [[http://www.youtube.com/watch?v=a5XNAC_2Mxg&feature=related Mermaid's Song of Sleep]] out of your brain!
** And Your Gravitation is this and CrowningMusicOfAwesome.
* EnsembleDarkhorse:
** Akeno Shiranui, among the few members of Nagasumi's harem with CharacterDevelopment.
* HoYay: Kai and Chimp. Plus Nagasumi's [[EvenTheGuysWantHim man-crush on Masa.]]
* LesYay: Sun and Lunar, Sun and Akeno, Mawari and Sun ''&'' Mawari and Akeno all have moments. And the Class President tends to unwittingly have them with the other girls too, much to her dismay.
* {{Moe}}: In one episode, Lunar's father, Gozaburo, and Masa (on orders) crossdress as schoolgirls and catgirls and act out moe stereotypes in an attempt to understand a girl's heart. [[FanDisservice It really is that horrible.]] Ends with Sun suddenly receiving cat ears, which everyone agrees is incredibly moe (before [[MegatonPunch being blasted away]]).
* NightmareFuel: The second half of the 2nd OVA, which does a GenreShift from comedy/action to straight horror, borrowing elements from TheRing. Saturn will probably haunt your nightmares now.
** The part of the TV series were Sun's family is knocked out by the creeper mermaid noble just because he wanted Sun for his own petty desires the terror on the Seto clan's faces as the special incense works to knocks them out and Ren crying out for her daughter to run away but they all wind up being knocked out.
* TheScrappy:
** Hideyoshi "Chimp" Sarutobi and Kai Mikawa. Sarutobi's development was completely lacking (and is only in this series to irritate the viewers), and Mikawa's refusal to accept that he can never be with Sun, and his attempts to bribe others, [[spoiler:not to mention his fraudulent death campaign in episode 24]], don't make for a likable character. And the duo's relationship doesn't help much, either.
** Pretty much the entirety of the Seto outfit (particularly Maki and Gozaburo), except for Sun, Ren, and Masa. Their sole purpose in this series is to try and keep Nagasumi and Sun's relationship in check, even if they have to resort to violence and think nothing of it.
** Lunar's father late in the series, to a lesser extent.
* {{Woolseyism}}: That whole chivalry/mermaid pun is instead rendered as "honor among thieves is honor under the seas" in the English version and thus [[IncrediblyLamePun drowned and made to fishfood]]. But then again, while "mermaid" and "chivalry" may be similar words in Japanese, they aren't even close in english, [[BlindIdiotTranslation so keeping it would have hurt the dub more than helped]].
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