"Will you descend into Hell with me?"
— Kaminoi Youko to Aratsugu Yorino
Semelparous (セメルパルス) is a Dark Fantasy Yuri Genre manga series by Jun Ogino (creator of Gamma). The series is an expanded rework of Ogino's 2016 one-shot "Tagai No Guardian" and began serialization in Comic Yuri Hime on 18 November 2019. An English localization by Seven Seas Entertainment was published beginning 14 December 2021.
Unbeknownst to the people of present-day Japan, Earth is under threat of invasion by humanoid kaiju from a Parallel Universe, and so for hundreds of years, an order of warriors called Bulwarks have secretly fought in the Void Between the Worlds to keep them from breaking through into our world. Aratsugu Yorino and her childhood friend Haruka have trained all their lives to join the Bulwarks, but then Haruka is tragically killed when a kaiju appears during a training exercise.
Left alone, Yorino continues her training and graduates at the top of her class and is assigned to Unit 3 Captain Kaminoi Youko for field training. As they slay the kaiju together, Yorino must face up to both the horror of the Forever War and her burgeoning feelings for her mentor.
Tropes:
- Adaptation Expansion: Semelparous is loosely based on an earlier oneshot by the same mangaka, "Tagai no Guardian".
- Ecchi: The series is quite frank and undeniably fanservicey about female sexuality, with a number of Shower Scenes, a couple of softcore masturbation scenes involving Kitamura, and eventually softcore girl-on-girl sex scenes. Somewhat oddly given the extent of the sexual content, Seven Seas rated it "Older Teen (17+)", rather than grouping it as "Mature" and printing it under their Ghost Ship imprint.
- Foreign Language Title: The Japanese title of the series is just the word "semelparous" in katakana. It's a biological term describing species that only reproduce once in their lives (salmon for example).
- Foreshadowing: In early chapters, the local news reports on people dying of sudden heart attacks. The kaiju are bioengineered war machines that have humans from the alternate universe in their heads controlling them, and when the human inside is killed, so is their Doppelgänger on this side. Yorino realizes this after one of her friends dies suddenly, while Youko killed her own sister's double.
- Good Thing You Can Heal: Pureblood mures are able to heal from grievous wounds by drawing energy from the walls.
- Gravity Screw: In the Void Between the Worlds, the "walls" actually behave like floors: each has its own gravity effect. Pureblood mures, and kaiju (which contain mure cells), are able to cross the midpoint where they cancel out and are attracted to the opposite wall, but Bulwarks cannot: they always fall back to the wall they came from.
- Homosexual Reproduction: Mures are able to conceive with human-mure Uneven Hybrid Bulwarks by taking the Bulwark's Aegis into themselves. In the case of Yorino's parents, both partners were female. After learning this, Yorino mentions the possibility that she might get pregnant with her girlfriend Youko while having sex with her.
- Human Aliens: The mures, a race that once lived in the Void Between the Worlds until a Civil War led to them conquering the other world, with their dissidents fleeing to ours and creating the Bulwarks to keep the others out. Mures are externally indistinguishable from humans but can pass through the walls between the worlds.
- Masturbation Means Sexual Frustration: Kitamura has a serious crush on Yorino and is shown masturbating to a fantasy of her in a couple of chapters. She has approximately zero chance of being able to consummate her crush given the Teacher/Student Romance between Yorino and Youko.
- More Experienced Chases the Innocent: Kaminoi Youko is in her twenties and certainly more sure of herself than the virginal Aratsugu Yorino. After they're partnered up, they quickly engage in a Teacher/Student Romance. The story doesn't directly state that Youko has had prior lovers, but the first time they have sex in volume 3, it's stated that Yorino has never even had an orgasm by herself before whereas Youko, who's the one who initiated and is leading their lovemaking, clearly knows what she's doing.
- Mutual Kill: The mures kill Youko in chapter 14 by creating a human-type kaiju out of her own Doppelgänger—meaning it could kill her simply by committing suicide. They end up running each other through.
- Never the Selves Shall Meet: The Alternate Universe has all the same people as the prime universe, but normally the walls between the worlds keep the death of one from affecting the other. However, if they die in the Void Between the Worlds, so does their counterpart: it takes two walls to fully isolate the counterparts from each other—and the kaiju are made from humans, meaning every time the Bulwarks kill a kaiju, somebody in our world dies. The mures of the other world weaponize this, making kaiju out of the doubles of friends and family of the Bulwarks to psychologically torture them, and, when possible, the Bulwarks themselves, to ensure a kill.
- Not Quite Dead: As revealed in Chapters 17 and 18, Youko ends up surviving the Mutual Kill scenario with her doppleganger by accidentally bodyjacking her double. She's brought back to the mures' world where she's recruited into La Résistance in order to try and stop the Big Bad.
- Recycled with a Gimmick: If you were looking for a yuri version of Attack on Titan, you're probably in the right place: the two series have a lot of thematic and conceptual similarities.
- Sexually Transmitted Superpowers: Inverted. Yorino's birth mother Mikoto, a pureblood mure, conceived her by taking her lover Maya's Aegis into herself. This caused Maya's powers as a Bulwark to weaken and eventually disappear by the time Yorino turned four.
- Sole Survivor: The Bulwarks are descended from humans and a faction of mures that, in roughly the mid-19th century, lost a war against another faction that turned Multiversal Conqueror and fled from the Void Between the Worlds into our universe. Unbeknownst even to herself at the start of the series, Yorino is the last pureblooded mure on "our" side after her birth mother was killed in action when she was four.
- Teacher/Student Romance: As a rookie Bulwark, Yorino is partnered to Unit 3 captain Youko for seasoning. The two women fall hard for each other and become a terrifyingly effective Battle Couple.
- Uneven Hybrid: The Bulwarks are humans with partial mure ancestry, which allows them to cross the wall from our world to the void—though it takes a pure mure to get all the way across to the Alternate Universe.
