Sundome

Kurumi: I won't have sex with you. Even if I do it with someone else... or as a casual fling... even if we were the last two people on Earth... I'd still never have sex with you. No matter how much you cried and begged for me... I'd never let you come. Are you... okay with that?
Aiba: ... yes.

Sundome (Stopping the Moment Before) is a Seinen manga by Kazuto Okada, who also authored Kyoukasho Ni Nai.

The main character is Hideo Aiba, who believes that all humans have specific turn-ons and, because of his specific demands, he has never "fallen in love with someone at first sight". Enter New Transfer Student Kurumi Sahana. She is odd, yet "all of her" is Aiba's turn-on. She gets a seat next to him, and the other students note Aiba's lack of interest in 3D girls. After school, Aiba is a member of the "Roman Club", whose members search for UFOs, paranormal activities and the like. The Roman Club was funded by school alumni now involved in all facets of Japan's politics and economics. Also, every member has a specific fetish and losing your virginity means you get kicked out of the club. For those members who uphold the rule of remaining a virgin until graduation, the alumni supply numerous recommendations and backups for getting into colleges and high-paying careers. However, due to so-called assassins, women sent by Roman Club alumni to cater to the Club members' fetishes and rob them of their virginities, six years have passed without a single member successfully graduating. As Aiba tries to get out of his membership, Kurumi shows up, showing an interest in the club. After the other members leave, Kurumi starts reading "The Secret Book of Masturbation", which she found in the club, and asks Aiba, "Show me how you jerk off." This is the start of an unusual relationship.

Tropes used in Sundome include:

A Date with Rosie Palms: All over the place.
- Jizzed in My Pants: Also all over the place. Sometimes literally.
Am I Just a Toy to You?: Aiba goes through a lot of this, especially after noticing the shoes in Kurumi's apartment.
Ass Shove: The ex-president has an anal fetish and is obsessed with sticking things up his and other people's asses.
Bland-Name Product: "Adides".
Cargo Ship: Tatsuya and his dolls.
Cassandra Truth: The Ex-President repeatedly declares that Kyouko and Kurumi are 'assassins'. He's only half right.
Cerebus Syndrome: The story begins with typical high school comedy, but gradually shifts more towards the melancholy. Then comes Collar 72...
Cloudcuckoolander: Everyone in the Roman Club has their head firmly in the clouds.
Contemptible Cover: This IS a manga that explores human sexuality, after all.
Darkskinned Blonde/Dumb Blonde: Kyouko.
Dirty Coward: Tatsuya. Played for Laughs.
The Ditz: Kyouko again.
Dumbass Has a Point: She gets words mixed up all the time, but Kyouko isn't always wrong.
Ecchi
Fetish Fuel / Fetish Retardant: Hoo boy. Aiba and Kurumi do a lot of sexual things. A LOT. What tends to make or break it for the audience is Aiba's urolagnia (read: golden shower) fetish.
First Girl Wins: Subverted, possibly double subverted. The woman that Aiba is with at the end of the manga does not seem to be Kurumi, but Aiba has some sort of sexual malfunction at the end, presumably a failure to get an erection. This implies that he never got over Kurumi.
Flower Motifs: Aiba flips out when someone leaves a bouquet on Kurumi's desk, implying that she died. Additionally, in the final chapter, Aiba has sex with Kurumi as the 'sea flowers' form on the shore. Kurumi notes that the flowers are made of dead plankton.
Gag Boobs: Kyouko.
Gag Lips: Katsu.
Idiosyncratic Episode Naming: Instead of chapters, we have collars.
Ill Girl: Kurumi.
Improbable Hairstyle: What is up with the ex-president's hair?
It Makes Sense in Context: Read the part about the 'assassins' again.
Malaproper: How did Kyouko make it to high school?
Male Gaze: Centered directly on Kurumi and Kyouko.
Manic Pixie Dream Girl: Kurumi.
A Man Is Not a Virgin: Inverting this trope is the entire point of The Roman Club.
Ms. Fanservice: See Male Gaze.
Mistress and Servant Boy: Aiba and Kurumi have this dynamic, despite being roughly the same age.
The Movie: Was adapted into four live-action movies.
Nerd Glasses: Katsu.
No Export for You: Averted, surprisingly.
No Name Given: The ex-club president.
Only Sane Man: Aiba and Katsu. Sometimes, just Aiba.
Panty Shot
Petite Pride: Aiba isn't interested in busty girls. Or any girl other than Kurumi.
Pettanko: Kurumi.
The Promise: Kurumi's declaration to Aiba at the top of the page. Aiba also promises to take Kurumi to see the sea flowers in the spring. Aiba keeps his promise; Kurumi does not.
Really Gets Around: Kyouko, though since she started hanging around the Roman Club, she's toned it down somewhat.
Scenery Censor: Katsu's fetish
Single-Target Sexuality: Aiba, Aiba, Aiba.
Snow Means Death: Collars 73-76 take place in the winter.
Wham! Episode: The aforementioned Collar 72.
Wham! Line: "Little did I know, that was the last summer I would spend with Kurumi-kun." It marks the shift from Shonen hijinks to the actual Seinen form that the manga ultimately takes.
Will They or Won't They?: Played with. Aiba and Kurumi have a relationship that's fraught with sexual tension and all manner of unconventional expressions of love, but they do have relationship. Additionally, Kurumi flat out says that she loves Aiba. Despite that, there's literal unresolved sexual tension, in that Kurumi controls when Aiba can orgasm. Katsu and Kyouko qualify as a straighter example..