Hekikai no AiON

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 now 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, known for Karin and Oniichan Control. The series is currently being translated by Tokyo Pop under the name Aion.

Not to be confused with the game Aion.

Tropes this series provide are:

 * Adventures in Coma Land: Tatsuya went into induced dream in order to wake her up.
 * All Just a Dream: according to Shizuki in a ,somehow, spooky way.
 * Affably Evil: Ariel, the eldest of the mermaid sisters, is less of a Jerkass than the rest of her sisters and she genuinely cares about Sheila
 * All Love Is Unrequited: Yoshiyuki is in love with Tatsuya who is in love with Seine
 * Attack of the 50 Foot Whatever:
 * Art Evolution: Compare this with this
 * Barbie Doll Anatomy
 * Betty and Veronica:
 * Played straight with Yoshiyuki as Unlucky Childhood Friend Betty and Seine as Action Girl Veronica.
 * Then played with; Shrinking Violet but exotic mermaid and human but Broken Bird witch. Though Tatsuya shows more attraction to Seine, he still can leave  alone when she's in trouble...
 * Big Bad: The evil mermaids.
 * Bigger Bad:
 * Big Fancy House: Tatsuya and Seine live in one of this. Later, Shizuki and Yuzuki join in.
 * Bishounen: 19-years-old Tatsuya. Minato also counts, with or without Time Skip
 * Bloodless Carnage: Averted. When Seine is killed, she bleeds as any normal person would do.
 * Blood Splattered Wedding Dress: Not a wedding dress but a kimono; still the same impact
 * Brainwashed and Crazy: All the victims of the mushis become this when they take a look at Seine's face.
 * Breather Episode: Chapter 28. It's even called "Renewing Moods"
 * Clothing Damage: Deconstructed with all the wounds Seine got
 * Covert Pervert: Everybody has their thing.
 * Yuzuki is a Lolicon.
 * Shizuki likes old men.
 * Yoshiyuki gets too excited after seeing Tatsuya in a Meido costume and a wig
 * likes to raise little girls.
 * Tatsuya gets too excited after
 * Crossover: With Karin
 * Cycle of Revenge: Seine, looking for avenge Shimon, kills a mermaid in an Off With Her Head way; later that same mermaid comes back from the dead looking for revenge, staring the cycle all over again
 * Enforced Cold War: . No wonder why he ended 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
 * Also, everybody starts to see that Tatsuya feels something for Seine
 * Expy:
 * Seine looks like Karin but with longer, green hair and as an Emotionless Girl instead of a Shrinking Violet.
 * Yoshiyuki is also this for Maki of the same series.
 * Minato looks like a younger, black haired version of Ren.
 * Tatsuya kinda looks like a Male!Asami, Asami is from Kagesaki-sensei's Sakura No Ichiban!
 * Face Fault: Minato had this in chapter 9.
 * Fan Service 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
 * Final Speech: "A man of the Tsugawa Family must be a high caliber man!!"
 * Furo Scene: Seine had one in chapter 3. Yoshiyuki had it in chapter 7
 * Girl in A Box: Seine, before moving to Tatsuya's house
 * Going Commando: Seine spends half of the 5th chapter without panties because this 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: Poised 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 some greek words.
 * Hearing Voices: As The Mushis manifest to the host after seeing Seine
 * Hellish Pupils: All the mermaids have them.
 * I'm a Humanitarian: The evil mermaids ate
 * Innocent Cohabitation: Tatsuya and Seine, who now moved in with Tatsuya.
 * Innocent Fanservice Girl: Seine, being an Emotionless Girl who consideres herself as a monster, is not bothered if somebody sees her shirtless or grabs her chest and she even takes her clothes up once to show Tatsuya that her wounds are healed. Of course, even if she doesn't freak out, Tatsuya does.
 * Sheila counts too,  and of course Tatsuya gives her the classic Please Put Some Clothes On scream.
 * Jerkass: All the mermaids except Ariel.
 * Laser Guided Amnesia: Everybody who had a Mushi taked off by Seine doesn't remember anything about their hatred to her
 * Lolicon:
 * Yuzuki is acknowledged as this, Played for Laughs and Les Yay, of course.
 * 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
 * Mayfly December Romance: Tatsuya one-sided crush on Seine.
 * Meet Cute: Tatsuya first saw Seine after she steps on his money when a couple of bullies throw it to the ground.
 * Mermaid Problem: Played for Drama...but in a very hilarious way
 * Mind Control Device: The Mushis.
 * 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.
 * Our Mermaids Are Different: The evil mermaids.
 * Panty Shot: Seine had this in the first chapter.
 * Pretty Freeloaders: Seine, Shizuki and Yuzuki (for a while) and, after Time Skip, . Tatsuya, apparently, has a thing for picking up girls to live in his house.
 * Returning the Handkerchief: Tatsuya used this as an excuse to talk to Seine at the first chapter
 * Ridiculously Cute Critter: Chibi Piyo-Piyo
 * Rule of Three: Seine can die just three time per day. If she dies more than that, Aion has to "recharge" itself  before she can use Aion again.
 * 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
 * Pool Episode: It gives us a great reveal...
 * School Festival
 * Shipper On Deck: Minagi seem 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.
 * 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.
 * Time Skip: Volume 8 starts 4 years since the events of volume 7. Everybody grows older...except Seine
 * 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.
 * Water Works: A lot of people cry in this manga but Tatsuya is more prone to it.
 * You Gotta Have Blue Hair:
 * Seine, who has green hair.
 * Yoshiyuki, who has purple hair.
 * Your Approval Fills Me With Shame: Seine got no other option but rip the Mushis out of a crowd of Brainwashed and Crazy students without excite the Mushis first. Shizuki applause this act. Seine was not amused since she know what doing that means.
 * Zettai Ryouiki: Seine wears rank B.
 * Your Approval Fills Me With Shame: Seine got no other option but rip the Mushis out of a crowd of Brainwashed and Crazy students without excite the Mushis first. Shizuki applause this act. Seine was not amused since she know what doing that means.
 * Zettai Ryouiki: Seine wears rank B.