* 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: Your Gravitation, the Song of Heroes and the Song of War.
* 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.
* MemeticSexGod: Masa.
* MoeMoe: In one episode, Lunar-papa, Gozaburo, and Masa (ordered to) 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.
* {{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]].
* TheyWastedAPerfectlyGoodPlot: Nagasumi's relationships with [[UnluckyChildhoodFriend Mawari]] and [[DefrostingIceQueen Lunar]]. They both obviously have feelings for Nagasumi, yet all the development[[note]]Episodes 4,6, and 18 for Mawari, and 12 and 13 for Lunar; Lunar was also technically the first girl to confess her true feelings to Nagasumi as well.[[/note]] between them was never spoken of ever again after a certain point, and they reverted to how they were before said development. Which is sad really, as that would've made the plot more interesting.