History Characters / HekikaiNoAiOn

* TheGadfly

* HeroicWillpower[=/=]ThePowerOfLove: Why he doesn't [[spoiler:kill Seine even after being infected.]]

Miyazaki Seine is a 300 year old girl with an immortal body who Tatsuya invites to live in his home; before that she lived in a cardboard box in a park. In the first chapter, Seine looks like a masochist because she seems to like being bullied. Actually, she becomes close to people who are infected by "mushis", a kind of parasitic, mind-controlling bugs, in order to hunt them. Her hunting ways go against the kind and pacifist Tatsuya's beliefs. Her motive is to avenge her foster father Simon's death by killing the people of sea, the mermaids. She controls a black snake called Aion that lives inside her. Her weakness is her inability to swim.

Miyazaki Seine is a 300 year old girl with an immortal body who Tatsuya invites to live in his home; before that she lived in a cardboard box in a park. In the first episode, Seine looks like a masochist because she seems to like being bullied. Actually, she becomes close to people who are infected by "mushis", a kind of parasitic, mind-controlling bugs, in order to hunt them. Her hunting ways go against the kind and pacifist Tatsuya's beliefs. Her motive is to avenge her foster father Simon's death by killing the people of sea, the mermaids. She controls a black snake called Aion that lives inside her. Her weakness is her inability to swim.

* HeroicWillpower[=/=]ThePowerOfLove: Wyhy he doen't [[spoiler:kill Seine even after being infected.]]

* ShowTheForehead

* [[spoiler:SheIsAllGrownUp]]

* [[spoiler:BadassTransplant]]: Enati. Subverted.

** ShinyMidnightBlack: With purple undertones.

* {{Expy}}: Of Maki from {{Karin}}. They have a similar appearance to each other and are childhood friends to the main character. Nagisa's BelligerentSexualTension with Minagi also parallels to Maki and Yuuji's SlapSlapKiss relationship.

* SecretKeeper

* {{Expy}}: Of Maki from {{Karin}}. They have a similar appearance to each other and are childhood friends to the main character. Nagisa's BelligerantSexualTension with Minagi also parallels to Maki and Yuuji's SlapSlapKiss relationship.

* BoyNextDoor: To Nagisa, and he knows how to milk the situation, always inviting himself to breakfast at her house.

* BerserkerTears / BrokenTears: Cried these while [[spoiler:[[BrainwashedAndCrazy choking Seine to death]]]].

* DamselInDistress: [[spoiler:When she was infected by Mushis.]]
* {{Expy}}: Of Maki from {{Karin}}.

* GirlNextDoor: She is Minato's neighbor.

* {{Neet}}:Sshe does absolutely nothing but eat and sleep. Partially justified as she's an IllGirl.

* {{Neet}}: she does absolutely nothing but eat and sleep. Partially justified as she's an IllGirl.

* PointyEars

*** StockingFiller
* MsFanservice:
** Bikini in the PoolEpisode.
** Her {{Meido}} outfit at "work".
** PantyFighter
* MulticoloredHair: Black with blonde bangs.
* NoSenseOfDirection: She gets lost inside a school, mostly because of her ditziness.
* OjouRinglets

* PointyEars

* GoingCommando / VaporWear: She seem to doesn't know what a bra is or what it's for.

* [[spoiler:OurMermaidsAreDifferent]]

* SchoolUniformsAreTheNewBlack: She wears her school uniform even when she's not in school since it's the only outfit she has prior to living with Tatsuya.

* BoundAndGagged: [[spoiler:For her own parents, when they were {{brainwashed and crazy}}]].

* WeaksauceWeakness: She's allergic to dog hair.

* HairColorDissonance: Is she a brunette or a dark blonde? Or even a strawberry blonde?
* HilariouslyAbusiveChildhood: Sorta. Her father wants to pay off his debts by [[KissingCousins marrying her to Tatsuya]] and getting at Tatsuya's inheritance; she declares [[ParentalNeglect her parents barely pay attention to her]] and just worry about money, and [[ParentsAsPeople when they try to care, they just shame her]]. All PlayedForLaughs.

* EyesOfGold

* EyesOfGold / HazelEyes: Normally.

* HazelEyes

* BlueEyes

A protege of Tatsuya's father and Tsugawa's family lawyer in charge of Tatsuya's money until he gets older enough. He and Tatsuya have a fraternal relationship, even though they are not blood relatives. He cares and looks after Tatsuya but his job as a lawyer prevents him from being able to be close to him.

A protege of Tatsuya's father. He and Tatsuya have a fraternal relationship, even though they are not blood relatives. He cares and looks after Tatsuya but his job as a lawyer prevents him from being able to be close to him.

Tatsuya's little second cousin.

* ThrowTheDogABone: [[spoiler:Ariel give her Enati's lower body after she died so now she's a complete mermaid again]].

* TragicKeepsake: She conserved the necklace that Nagisa chose and Tatsuya buy for her [[spoiler: even after returning eternally to the sea]].

* [[spoiler:RelationshipUpgrade[=/=]OfficialCouple]]
*** [[spoiler:TogetherInDeath]]