Rouge Noir

When Ayane Tezuka was 19, she was a cute college student aiming to be a piano player. In these days she also was the private tutor of a young rich boy, Kou Narumiya, and sparks simply flew between them! However, not only Kou was from one of the richest families in Japan but he was only 14, despite being much Younger Than They Look. Once Kou's mother noticed and harshly warned Ayane to not get too close to Kou, such an attraction ended up in... well, not good terms.

Flashforward to six years. 25-year-old Ayane is now a beautiful school teacher in an all-girls school and her life seems to be placid and perfect, but she hasn't really forgotten Kou. All of a sudden, while attending a jazz-piano audition, she finds the now older Kou again. Old feelings sort-of return, and Ayane's heart is a mess from then on...

Rouge Noir is a short jousei manga by Kyouko Mizutani, spanning two volumes. If you wish, you can read it here.

Tropes used in Rouge Noir include:

Alpha Bitch - Bitch in Sheep's Clothing: Rena Morikawa, the star of the school chorus that Ayane directs. Not only she falsely accuses Kou of trying to rape her (which is ironic, considering what he did do years ago), but she also leaks info about him and Ayane to the Headmaster of the school out of spite.
Big Fancy House: Kou's.
Broken Bird: Ayane has more issues than you'd think.
Chekhov's Gun: Ayane once plays the piano for Kou while tutoring him. Kou later plays the same piano song in the Evans club's opening
Chekhov's Gunman: Sorta: two of Ayane's coworkers, Shibasaki and Okamura, are featured in another short story from Mizutani.
Don't You Dare Pity Me!: Ayane, when she leans that Kou din't take up the jazz-piano job because of her.
Elegant Classical Musician: Both Kou and Ayane, in different degrees. Both are talented pianists, and Ayane is also a pretty decent singer.
Expository Hairstyle Change: Ayane used to have Rapunzel Hair at age 19. At age 25 she has a much shorter cut.
Green-Eyed Monster: What made Kou snap on Ayane and rape her was seeing her with Naoto after he had called her to his cell in the middle of an Heroic BSOD and she didn't reply. (Because Naoto had found her cellphone and deleted his messages).
Grey Rain of Depression: When Ayane breaks up with Naoto, she does it via a cell call under the rain.
He's All Grown Up: Kou, and how.
- And his pup Ryuunosuke, too. Ayane met her when she was a puppy, then as a big Shiba dog.
Heroic BSOD: Ayane, after Kou rapes her. Kou has one of his own immediately afterwards, when she's gone and what he did to her fully sinks in.
Hot for Student: Played with. When Ayane was Kou's tutor, there was UST between them but nothing came out of it. Or so it seemed. Six years later, when they meet again, he still calls her "sensei".
Hot Teacher: Ayane and her boyfriend Naoto. Kou later becomes a student teacher in their workplace.
Josei
Just a Kid: Kou has big problems with that, to the point of a Berserk Button. He ends up pretty much raping Ayane and giving her a "The Reason You Suck" Speech, which is the reason why she stopped giving him classes.
Love Hurts
May-December Romance: May September (five years), and unusually the woman is the older one.
Meganekko: Ayane
Modesty Bedsheet: Ayane, as she goes downstairs after she and Kou have (consensual) sex.
Near-Rape Experience: When Ayane goes to Kou's house after he's (falsely) accused of trying to rape Rena, he pins her to the bed. When Ayane tells him the same words she told him before he raped her years ago and admit that she's jealous of Rena, Kou stops himself and lets her go.
Rape Is Love: Discussed. Ayane aknowledges her and Kou's sexual encounter years ago as rape, and yet she also admits to having feelings for him.

" Six years ago, Kou violated me. (...) Even I think there's something wrong with me. (...) That sound and Kou himself, despite the calamitous past that we have, are drawing me in."

- And later when Kou and Ayane declare their mutual love and have sex willingly, Kou reveals that he has been feeling guilty ever since then and apologizes profusely to her.
Rescue Romance: Kou helps Ayane when she's harrassed by a drunkard.
Romantic False Lead: Naoto
Scarpia Ultimatum: Sorta. Naoto knows Kou didn't try to rape Rena, but he blackmails Ayane with it: he'll only testify in Kou's favor if she accepts to marry him. He later backs off and testifies anyway.
Sensei-chan: "Ayane-cchi", though not as much as others.
Shower of Angst: Ayane, after being raped by Kou.
Sugar and Ice Guy: Ayane thinks Kou is this.
Tomboyish Name: Ryuunosuke is actually a girl puppy.
Unwitting Instigator of Doom: Had Naoto not picked up Ayane's cellphone and deleted Kou's messages for her due to outta jealousy, nothing would've happened in the end.
What the Hell, Hero?: Kou towards Rena, when she tells him she ratted them out.

"What a pitiful woman! Are you only capable of finding happiness through the misfortune of others?!"

The White Prince: Kou, son of a VERY wealthy tycoon from the aviation business
Wounded Gazelle Gambit: Kou is accused of trying to rape a girl named Rena Morikawa. It turns out that, in the end, it was this: Rena wanted to "help" Naoto to "clean up competition" and take Kou "out" so he'd have the way cleared to win Ayane's affections. It doesn't really work anyway, since Naoto sees that Ayane was more feisty than he thought.
Yonkoma: The Wanderful Life omakes featuring Ryuunosuke.