Taimanin Asagi 3 (visual novel)

A 2012 Hentai Visual Novel by Anime Lilith, Taimanin Asagi 3 is the third main installment of the series about demon-fighting ninjas in skintight catsuits.

Ten years after the first game, the Taimanins keep their fight going against the forces of darkness lurking inside Japan. The anti-demon ninja Asagi has taken to herself the role of raising the brother of her deceased lover Kousuke, a survivor of a massacre of his clan. She raised him along Asuka, another survivor of the same incident, but Asuka left the Gosha village, the home and training center of the Taimanins, two years before the game starts and, though she keeps fighting for good, she is for unexplained reasons hostile to Asagi, and works alone.

Meanwhile, Kiryuu, the main "hero" of Taimanin Murasaki ~Kunoichi Kugutsu Dorei ni Otsu~, has fully integrated into the Gosha village as scientist. Murasaki constantly abuses him, but he loves it.

Kousuke, however, has less-than-holy feelings for his adoptive mother, and uses his special powers to make her aroused. Despite deeming their relationship "forbidden", Asagi nonetheless engages on a secret relationship with him after he uses his powers on her and she enjoys it. However, there is a secret behind Kousuke's powers: he awakened them after taking medication from the mysterious doctor called Muroi, and not naturally like all the other Taimanins.

After Kousuke discovers Asagi is pregnant through a pregnancy test given to him by Muroi, the paper used in the test proves itself to be a trap that transforms Kousuke to a human-like meatball, like his brother one decade before. Muroi reveals himself to be Fulst, a subordinate of Edwin Black, Asagi's arch-enemy. He and a resurrected Oboro(as already shown by the end of the second game) are however unable to kidnap Asagi as Edwin Black ordered them to, thanks to Murasaki and Kyriuu's timely intervention, but take Kousuke hostage.

Afflicted with guilt by yet again allowing the man she loves to be kidnapped by Oboro, Asagi, Murasaki, and Asagi's sister Sakura set out to rescue Kousuke.

Directed by Sasayama Ittousai, that also directed Taimanin Yukikaze. Published by Anime Lilith. Adapted in a two-episode OVA in 2016.

Tropes used in Taimanin Asagi 3 (visual novel) include:

Absurdly Youthful Mother: Asagi doesn't look that much older than her adopted teenage children, Asuka and Kousuke.
Artificial Limbs: Asuka's legs and arms were replaced with cybernetic limbs. That allows her a large amount of flexibility compared to most Taimanins in term of weapons.
Baby Got Back: Asuka notices Kousuke is attracted to her butt.
Big Bad: Edwin Black is the one behind Fulst's plot.
Blow You Away: Asuka's Taimanin Art involves the manipulation of wind.
Brother-Sister Incest: Downplayed. Asuka and Kousuke aren't biologically related. They are only siblings by virtue of being adopted by the same woman, Asagi. Asuka is attracted to him but Kousuke seems to not have much more attraction to her than he would have for any other pretty girl with a curvy body.
Cyborg: Asuka has mechanical limbs to compensate for the ones who she lost during a mission.
Depraved Homosexual: One of the first insults Asagi throws at Fulst is the he is a homo. A homo that rapes boys.
Eagleland: Heavily implied to be Type 2, as the United States is under control of Nomad, that is controlled by Edwin Black.
Evil Mentor: Fulst is Kiryuu's mentor and a rapist, torturer and assassin who commits unethical legal experiments.
Fat Bastard: Fulst is fat and a pretty unethical cruel scientists, said to be also a pederast.
Fetus Terrible: Subverted. Given the series' penchant for Body Horror, the child Fulst uses to manipulate Asagi's body would be expected to be some kind of hostile, smart creature. It turns out to be completely defenseless and smart as any fetus, allowing a normal obstetrician to remove it surgically.
Good Girls Avoid Abortion: The game seems to imply Asagi don't would be against it as she only asks Kousuke's opinion if she would keep it or not, so it seems to be averted, but the discussion is squashed by Fulst revealing his trap, and the child ends up being aborted anyway because otherwise Asagi would be under the complete mercy of Fulst. Asagi's emotional state is not one of the best after it though, and she and her fellow allies avoid the topic.
Green-Eyed Monster: It's heavily implied Asuka is so hostile to Asagi because she is envious he is attracted to Asagi and not so much towards her.
Making Love in All the Wrong Places: Kousuke and Asagi have sex on the principal office of Gosha Academy, that is, Asagi's own office.
Man Child: Sakura's behaviour didn't change much in the decade between the first game and the third. Now at her 20s, therefore, she still acts pretty much like a kid.
Naughty Tentacles: Downplayed, but Kousuke's "Bedroom Art" manifests as spiritual tentacles that enter through the victim's body to cause sexual arousal.
Not That Kind of Doctor: Kiryuu is not a obstetrician, so an unnamed, unseen NPC extracts the fetus used by Fulst to control Asagi from her womb instead, with help of Murasaki.
Parental Incest: Asagi engages on a carnal relationship with her adopted son.
The Power of Love: Kousuke's love for Asagi is such that he actually awakens his real Taimanin power (magnetism) by fighting against Fulst's control over him to hurt Asagi through the baby in her womb.
Shameless Fanservice Girl: Invoked. Sakura has zero problems walking around in lingerie in a house with a teenage boy living in it, something Asagi mentions she warned hher against doing exactly because what would cause in him.
Shipper on Deck: Both Asagi and Sakura, despite disliking Kiryuu's personality, seem to want him to end up with Murasaki.
Token Evil Teammate: Kiryuu doesn't seem to have dropped his nasty personality and is still extremely proud of the body remodeling he did on Asagi and Sakura as he himself removes it, but he still works with the Taimanins without complaints. It is explained easily by his affection towards Murasaki, that he genuinely loves.
Victim Falls For Rapist: Downplayed, but Kiryuu is the dude who blackmailed Murasaki into sex, including taking her virginity, and in the present she is attracted towards him. Of course, this came after years of her having free reign to do whatever she wanted with him, so the trauma is long gone.