Animal X

Animal X is a lengthy Yaoi manga by mangaka Sugimoto Ami.

Yuuji Ayukawa is a meek 27-year-old man who has never been in control of his own life. From his fiancée lecturing him about his shyness and sensitivity to his position as glorified guinea pig at Endou Chemical, Yuuji is the quintessential Extreme Doormat.

One evening, he comes home to find that he has left a window in his room open. A wild young man who has just escaped government custody leaps out from beneath his bed and threatens to kill him. Yuuji's roommate, another in the long line of bullies Yuuji apologetically endures, bursts in... and is promptly decapitated by a fifteen-foot-tall T-rex. It turns out that Minato is a dinosauroid, a species that has long lived apart but parallel with humans, and he is capable of transforming into a reptilian killing machine under stress. Something has attracted him to Yuuji's room: Yuuji "smells like kin" and Minato is immediately overcome by an overwhelming desire to mate. From there, the story becomes the tale of various ancient conspiracies, corrupt researchers and executives, and Yuuji and Minato's evolving relationship.

And then Yuuji gets pregnant.

It is probably one of the least sensational uses of gender bending and M Preg since The Left Hand of Darkness.

Not to be confused with the Discovery Channel series about cryptozoological animals.

This series provides examples of:

 * Arranged Marriage: Yuuji and Kyouko
 * Bishounen: Minato and Yuuji.
 * Blooper: Minato loses an arm  and gets a mechanical replacement quite a few chapters later. During these chapters the missing arm magically reappears for two pages and then disappears again.
 * Body Horror:
 * Yuuji takes manifesting female reproductive organs pretty well, but is scared of the idea of carrying a child to term.
 * Later, he becomes detached and apathetic about his body as a coping mechanism for traumatic experiences. It's metaphysical Body Horror.
 * Break the Cutie: Between Morning Sickness, anemia, constant Even The Guys Want To Violently Violate Him, having to bear the child of the man who raped him, and both him and his family being pawns/targets in half a dozen gambits, Yuuji cannot catch a break.
 * He crosses the Despair Event Horizon when he finds out  After that, Yuuji is quietly broken and makes remarks that show that he's reached a point where he doesn't much care if he lives or dies.
 * Cute Little Fangs: Minato. And how!
 * Deus Angst Machina: By the tenth or fifteenth volume you'd be forgiven for thinking that the entire world has it in for Yuuji and Minato.
 * Dying Race: Minato's.
 * Hermaphrodite: Yuuji. "It feels like you're equipped for both."
 * Jumping the Gender Barrier: Yuuji and Minato are a good match, but Yuuji doesn't fall for Minato until after his transformation. He wonders if part of his heart has "become female too". See also The Mind Is the Plaything of The Body.
 * Mars Needs Women: Or, well, secret race of dinosaur people needs hermaphroditic hybrid.
 * Mate or Die: Minato is hellbent on propagating his Dying Race.
 * The Mind Is the Plaything of The Body: Yuuji eventually makes references to thoughts that he, at least, identifies as coming from his male or female halves.
 * Mister Seahorse: Yuuji
 * Ninja Pirate Zombie Robots: Police officers revived to hunt rogue dinosauroids. A (technically) zombie SWAT team. Yes. Even here, however, the series never breaks from its serious, thoughtful tone.
 * No Periods Period: Averted, naturally. Yuuji is... fully functional.
 * Pregnant Badass: A rare male example. Whether it's hormones or his newfound relationship with Minato, Yuuji becomes much more courageous, to the point of fully intending to take on a T-rex with nothing but a chainsaw.
 * Double Standard Rape Male On Male: Averted brutally.
 * Shown Their Work: Drumheller is a real town in Alberta, Canada, that claims to be 'The Dinosaur Capital of the World'. Even the landscapes are fairly accurate.
 * Victim Falls For Rapist - A staple Boys Love trope somewhat averted. Yuuji never falls in love with the ones who have their way with him, and Minato, who truly loves him, never goes that far.
 * It's oddly reversed in that the original rapist,, despite considering him nothing more than a conquest at the time, ends up falling for Yuuji and shows quite a bit of concern for their daughter . Yuuji eventually forgives him but does not return his feelings.
 * Yank the Dogs Chain:
 * Yaoi Guys: Yuuji and Minato, although Yuuji's biological reality raise the question of whether the series is, strictly speaking, "yaoi".
 * Minato initially identifies Yuuji as a female (by scent) but refers to him with masculine pronouns. And though Yuuji has always been somewhat "feminine" (cooking, sewing, submissive, etc, forgive the generalizations) and is very pretty, he has lived his life and thinks of himself as a male. It's yaoi.
 * On the one hand, he always distinguishes himself from women, on the other, he doesn't consider himself and Minato to be a gay couple. "Ah, no, if that were so then we couldn't have children, could we?"
 * You Wouldn't Like Me When I'm Angry: The dinosauroids turn into ... well... dinosaurs when stressed or angry, and not the sissy herbivore kind.