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Manga / Hekikai no AiON

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Tatsuya Tsugawa's parents die in an accident. One week after the accident, he has inherited millions of yen and is now starting high school. He tries to follow his father's last words about being a man of high caliber. A little while later, Tatsuya tries to rescue a girl, Seine Miyazaki, from being bullied. She coldly rebuffs his attempt and claims that she likes being bullied. He still tries to help her despite the fact she told him to leave her alone. It turns out that Seine is immortal, and she kills parasitic bugs that control humans with a snake named Aion that devours them.

Hekikai no AiON is a fantasy and horror manga by Yuna Kagesaki, who is also known for Sakura no Ichiban! and Karin. The series was serialized in Dragon Age from 2008 to 2012, with 11 volumes. Three volumes of the series were translated in English by Tokyopop under the name Aion before it eventually closed its North American publishing division.


Not to be confused with the game Aion.

Tropes this series provides are:

  • Accidental Pervert: Minagi accidentally walks into a naked Seine in the bathroom and freaks out because she was unaware that Tatsuya brought a stranger into the house.
  • Adventures in Comaland: Tatsuya went into Seine's induced dream in order to wake her up.
  • Because You Were Nice to Me:
    • Sheila, one of the evil mermaids, fell for Tatsuya because he was the only aside Ariel to show her kindness. Also, because she was afraid to lose him, she stopped thinking about avenging herself against Seine, the one who let her without voice and "killed" her.
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    • Our protagonist Seine as well. She decided to go with Shimon, a man she knew absolutely nothing about, just because he was nicer to her than her abusive foster father.
  • Betty and Veronica:
  • Big Bad: Ariel, the eldest of seven mermaid sisters, who periodically destroy major cities (usually by tsunami) to collect humans' psyche. And in the later parts of the story, Demiurge.
  • Bittersweet Ending: Tatsuya and Seine get the chance to have a Relationship Upgrade, the town is saved from being sunk, Enati's threat is avoided and Sheila gets to have a genuine mermaid lower body but has to sacrifice her human legs; Seine gets to kill 2 of seven mermaids, after hearing Simon's history through Ariel, and seems to give up her revenge. After many years, Tatsuya dies of old age and Seine is seen besides his grave, just as young as always.But then, Tatsuya's soul seems to come for Seine, and she gives up Aion. Both are Together in Death and Aion returns to its true owner, Sheila, returning her voice. This makes the end a little more sweet but still a Tear Jerker.
  • Bound and Gagged: Minagi gets bound and gagged by her parents (who were possessed by mushi) because she overheard them talking about killing Seine.
  • Brainwashed and Crazy: All the victims of the mushis become lose all rational thought when they take a look at Seine's face.
  • Breather Episode: Chapter 28. It's even called "Renewing Moods"
  • Cardboard Box Home: Seine lives in a cardboard box since she's Really 700 Years Old and has no family. Even after Tatsuya took her home, she still insists to sleep inside her beloved cardboard box.
  • Crossover: With Karin.
  • Cruel to Be Kind: Seine must force the Mushi's host into hate her and kill her so she can rip out the Mushi.
    Seine: "It's fine like this. She should hate me more. If she does, I can save her quickly."
  • Cycle of Revenge: Seine, looking for avenge Simon, kills a mermaid in an Off with Her Head! way; later that same mermaid comes Back from the Dead looking for revenge, starting the cycle all over again.
  • Enforced Cold War: Tatsuya forced Seine and Sheila to live under the same roof when Sheila left the sea. No wonder why he ended up being punched in the face.
  • Everyone Can See It: Well...everyone but Tatsuya can see that Yoshiyuki is in love with him. He's just that dense.
  • Fanservice with a Smile: Played for Laughs, since all the boys dress in Meido costumes. Tatsuya gets more focus since his skirt is too short because of him growing, and his weeping, red face.
  • First-Name Basis: When Tatsuya at first started calling Seine by her last name. After they started living together, She tells him to call her by her first name since she thinks Miyazaki is "made up". Also, Seine just calls him Tatsuya.
  • First Kiss / Sacred First Kiss: Seine and Minagi got their first kisses taken by Yuzuki
  • Foreshadowing: Tatsuya calls Seine "Seine-chan", she shivers at this. The reason? One of the twins calls her the same.
  • Four-Girl Ensemble: Yuzuki (The Ditz), Seine (Deadpan Snarker), Shizuki (The sexy one) and Sheila (Wild Card).
    • And Before Sheila appeared, Nagisa as the Wild Card.
  • Freudian Trio: Shizuki (manipulative Superego), Yuzuki (kind Ego) and Seine (vengeful Id).
    • Alternatively, Seine (Superego), Tatsuya (Ego) and Sheila (Id).
  • Furo Scene: Seine had one in chapter 3. Yoshiyuki had it in chapter 7
  • Gender Flip: This volume 10's omake.
  • Giant Wall of Watery Doom: The way the mermaids collet psyche...Also, Seine's image of death inside her mind.
  • Going Commando: Seine spends half of the 5th chapter without panties because they got ruined and she only had a pair.
  • Gorn: Cortesy of Brainwashed and Crazy people upon Seine. Let's make a list:
    • Chapter 2: Thrown off a building
    • Chapter 4: Poisoned and stabbed with a glass bottle
    • Chapter 8: Choked to death
    • Chapter 17: Batter Up! to death
    • Chapter 19 and 20: Impaled with Extreme Prejudice
    • Chapter 21: Stabbed with a knife in the lung
    • Chapter 22: Disarmed
  • Gratuitous Foreign Language: The mermaids (and Shizuki, sometimes) use greek words.
  • Grievous Bottley Harm: In chapter 4, Minagi's father stabs Seine with a bottle.
  • Hearing Voices: As the mushis manifest to the host after seeing Seine.
  • The Hecate Sisters: Yuzuki (ditzy maiden), Shizuki (eccentric mother), Seine (bitter crone).
  • Innocent Cohabitation: Tatsuya and Seine, who now moved in with Tatsuya.
  • Innocent Fanservice Girl:
    • Seine, being an Emotionless Girl who considers herself as a monster, is not bothered if somebody sees her shirtless or grabs her chest. Shehe even takes her clothes off once to show Tatsuya that her wounds are healed. Of course, even if she doesn't freak out, Tatsuya does.
    • Sheila counts too, as being a mermaid, she is shirtless all the time; every time she sees Tatsuya after getting her human form, she's naked and of course Tatsuya gives her the classic Please Put Some Clothes On scream.
  • Imagine Spot:
    • Tsukasa, every time someone says they are living with Tatsuya because he picks them up, has a imagine spot of them as cute, pitiful homeless girls under the snow.
    • Tatsuya also has one of Seine in a cute two-piece swimsuit after hearing they're going to the pool and Yuzuki seems to be watching it.
  • Jerkass: All the mermaids except Ariel.
  • Laser-Guided Amnesia: Everybody who had a Mushi taken off by Seine doesn't remember anything about their hatred towards her as long they get to kill her before The Mushi was taken off.
  • Love Triangle: Sheila -> Tatsuya -> Seine, making it type 5
  • Luminescent Blush: Tatsuya is prone to this. Also Yoshiyuki, Sheila, heck, even Seine
  • May–December Romance: Tatsuya's parents had an age loop of 30 years and still they were Happily Married
  • Meet Cute:
    • Tatsuya first saw Seine after she stepped on his money after a couple of bullies threw it to the ground.
    • Also, Tatsuya's parents. They met when he saw her hanging white radishes.
  • Mermaid Problem: Played for Drama...but in a very hilarious way
  • Mind-Control Device: The Mushis.
  • Modesty Towel: As improvised bikini.
  • More than Mind Control: Mushi infected Nagisa. Also Himenuma; though Mushi infected, he seems to have a crush on Sheila.
  • No Periods, Period: One day, Yoshiyuki was all mad, Minato jokes that it must be "that day of the month".
  • Not What It Looks Like: It has moments.
  • Omake: There're lots of this in each volume, where Kagesaki talks about ups and downs of her while making Aion.
  • Ominous Fog: Enati, the third mermaid can use fog to make an illusion of Simon.
  • Our Mermaids Are Different: The evil mermaids.
  • Pet the Dog: Seine comfort Tatsuya in the first chapter saying him he can become a high caliber man
  • Perverted Sniffing: Sheila smells Tatsuya's necktie.
  • Pinky Swear: Tatsuya and Sheila do a pinky swear when Tatsuya promises not to tell anyone that she's a mermaid.
  • Pretty Freeloaders: Seine, Shizuki and Yuzuki (for a while) and, after Time Skip, Sheila. Tatsuya, apparently, has a thing for picking up girls to live in his house.
  • Red Herring: The deal with Tatsuya's mother. Her name was Umi (which means "sea") and Sheila was very much a carbon copy of her image, so many readers thought Umi was a mermaid too. In reality Umi was just a normal human but her psyque was took by Sheila after her death so Tatsuya sometimes could "feel" his mother's scence in Sheila.
  • The Reveal: Why Tatsuya saw Sheila as his mother at one point? Because Sheila took her psyche when she died.
  • Returning the Handkerchief: Tatsuya used this as an excuse to talk to Seine at the first chapter
  • Reused Character Design:
    • Seine looks like Karin but with longer, green hair and as an Emotionless Girl instead of a Shrinking Violet.
    • Yoshiyuki is a purple haired version of Maki of the same series.
    • Minato looks like a younger, black haired version of Ren.
    • Also, everybody starts to see that Tatsuya feels something for Seine.
    • Tatsuya kinda looks like a Male version of Asami from Kagesaki's Sakura no Ichiban!
  • Rule of Three: Seine can die just three time per day. If she dies more than that, Aion has to "recharge" itself and Seine will feel the pain of all those deaths before she can use Aion again.
  • Running Gag: "Earthshake. There's been a lot of them these days."
  • Seiza Squirm:
    • In chapter 30, Tatsuya and Seine do this while talking to Tsukasa for midnight sneaking out of the house.
    • Also, Seine had cramps for sitting so long in seiza at Tatsuya's parents's funeral event.
  • Shipper on Deck: Minagi seems to like shipping Seine with Tatsuya. It helps that it's obvious the guy is really in love with the girl and she wants to help him.
  • Ship Tease: Seine and Tatsuya.
  • Shown Their Work: There was really a earthquake at Port Royal that sank 2/3 of the city into the sea.
    • Also, the mermaids can cause earthshakes from the sea; it's geologically possible that earthshakes provoke volcanic eruptions, therefore the mermaids did cause the Vesuvio eruption.
  • Sibling Rivalry: All the mermaids are sisters and some of them are trying to overpower her oldest sisters.
  • Swallowed Whole: The only way to rip off the mushi from the host's body is Aion swallowing the host to "eat" the mushi.
  • There Is Only One Bed: Shizuki and Yuzuki slept in the same bed Tsukasa was sleeping after getting hit on his head because how "High status" women like them would sleep on the floor?
  • Time Skip: Volume 8 starts 4 years since the events of volume 7. Everybody grows older...except Seine who's immortal of course.
  • Too Kinky to Torture:
    • At the first chapter, Minato warns Tatsuya about not messing around with Seine because he thinks she is a masochist who likes being bullied.
      • Hilariously "enforced" by Seine to keep Tatsuya off her neck.
    • After getting Impaled with Extreme Prejudice and removing one of the long stakes with Tatsuya's help, she had a Luminescent Blush and a dazed expression on her face. "A lot of endorphins were released". The position they had to take in order to get the stake out (him behind her, pushing her forward towards the wall that the end of the skewer was braced against) was more than a little suggestive to begin with...
  • Waterfall Puke: Tatsuya's food had this reaction on all people, except Seine. Meanwhile, it causes Shizuki to puke Blood from the Mouth.
  • Wham Episode: Volume 10. The whole Volume 10. Tatsuya shouts aloud he likes Seine, Sheila infects Tatsuya via stealing his first kiss and send him to kill Seine at her sisters's demand, Tatsuya doesn't kill Seine and instead pulls himself out the friend zone he has been for 4 years by kissing her, Sheila is returned to the sea by Ariel, Shizuki and Yuzuki came back, the fated day is closer...and Seine is dressed as a Meido
  • What Is This Thing You Call "Love"?: Seems to be the mermaids's case; specifically the emotional part of "love" since they do know "love" is used by humans to mate.
  • Your Approval Fills Me with Shame: Seine gets no other option but to rip the Mushis out of a crowd of Brainwashed and Crazy students without "exciting" the Mushis first. Shizuki applauds this act. Seine is not amused, since she knows what doing that means. Hosts who aren't able to satisfy the Mushi's urge to kill Seine find themselves still wanting to kill her, but with no idea why. This isn't good for their sanity.