Nisekoi

Raku Ichijou is your Ordinary High School Student. Well, as ordinary as he can be, being heir of a Yakuza family, a position he's not too happy about. Still, he lives a mostly carefree life until one day he crashes into (or, more precisely, is crashed into by) Chitoge Kirisaki - his class's new transfer student. This causes him to lose his most precious possession- a pendant given to him by his first love ten years earlier. Some harsh words are thrown and even though Chitoge eventually helps him find the pendant, the two of them are off to a bad start.

If that wasn't enough, a new gang shows up in town and start getting into fights with Raku's family - a conflict that could escalate into full-blown gang war. Through the power of coincidence, the gang's leader turns out to be not only Raku's father's old friend, but also Chitoge's dad! Together the two heads devise a plan to calm down their rowdy subordinates: Raku and Chitoge will have to pretend to be a couple! The two of them are not too happy about that, but agree to play along to avoid a bloody conflict.

Thus starts a story of love, lies, twists and promises. How long will Raku and Chitoge manage to fake their feelings? And how long will those feelings stay fake?

Tropes used in Nisekoi include:

All According to Plan: Marika uses this so often that Raku invokes it word-for-word after she'd kidnapped him to a tropical resort and then their small boat sank:

Raku: And I'll ask just to be sure, but ... "This was all according to plan" isn't going to be the next thing out of your mouth, right?
Marika (smiling): My, Raku-sama. What kind of idiot would plan for us to be stranded together on an uninhabited island? Kya♥
Raku: I asked you because I had a feeling that an idiot was standing right in front of me. You kidnapper.

Bifauxnen: Tsugumi. At first glance, people can't tell: "Is that a girl?" "You moron, look at how he's dressed. He's a guy." She is a girl. It doesn't help that she has the solely masculine given name "Seishirou."
Big Fancy House: Raku's, Chitoge's, Marika's (and then there's her mom's place). But the shocker is Ruri's great-grandfather's very traditional Japanese palatial estate.
Blind Without'Em: When Ruri misplaces her glasses, it's shown that she can't tell the difference between Raku and Kosaki at a distance of less than a meter. Not even the difference between the colors of the boys' and girls' school uniforms.
Bromantic Foil: Shuu Maiko, Raku's best friend. Half the time he meddles to help Raku. Other half- because he thinks it's funny.
Breaking the Fourth Wall: Done occasionally; for instance, in Chapter 112, a policeman last seen some five volumes before asks to speak with Marika:

Marika (looking over her shoulder at the readers, while waving towards the policeman): To the nearly 100% of the readers who have forgotten this person...I shall explain who this person is.

- Lampshaded in an earlier chapter which opens with Chitoge muttering a synopsis of the story; Tsugumi, in the background, asks, "Who are you speaking to?"
Cat Smile: Practically Shuu's default expression.
Censor Steam: Used repeatedly in Chapter 23.
Childhood Marriage Promise: One of the most important plot points is that Raku made one with a girl he knew ten years before the start of the series. Unfortunately he doesn't remember her name or face. His only lead is that she has the key to the lock in his pendant.
- It's revealed early on that Kosaki Onodera has a key from a childhood promise she made but seems unsure about.
- Later we find that Chitoge also made a promise with a boy whom she can't recall. In fact it's strongly implied that they made the promise with each other.
  - As of Chapter 27, Onodera claims to be the promised girl, when asked by Raku.
- In Chapter 118, Yui Kanakura shows up, and she has a key, too, although she denies knowing anything about promises.
Chronic Hero Syndrome/Samaritan Syndrome: Kosaki and Shuu both say Raku feels a compulsion to help others; "he can't leave people alone if they're in trouble." Shuu particularly mentions an incident when Raku moved with incredible speed to save a woman who was about to fall down a flight of steps.
Class Is in Room X-01: Despite how generic many of this series' other elements are, it averts this. The class the main cast is in is 1-C.
Clueless Chick Magnet: Raku. He even recognizes that the "symptoms" Tsugumi lists suggest she's in love -- but he doesn't catch on that he's the one causing her to react that way. This is just five chapters, and less than two weeks, after her arrival.
Covert Pervert: After a rocky start, Tsugumi ships Raku/Chitoge. But she also begins to involuntarily fantasize about having an affair with him behind Chitoge's back.
Crash Into Hello: Chitoge and Raku. Specifically, her knee crashes into his face when she jumps over a wall without thinking there might be someone on the other side.
Defrosting Ice Queen: From the start, Ruri has despised Shuu. Then in Chapter 128 she admits to herself that she feels "like something is getting caught in my chest" when he leaves her name out of the long list of girls he "loves."
- As of Chapter 209, she admits (again only to herself) she's fallen for him.
- And confesses in Chapter 223. Her smile then is the sweetest expression she's ever shown.
Exploding Closet: Chitoge's.
Fan Service: Kept at very low level considering the genre... until the 2 part Hot Springs Chapter that is.
First-Name Basis: Chitoge decides that she and Raku should call each other by their first names after he saves her in the forest.
Forgotten First Meeting: Ten years before the main action starts, Raku, Chitoge, Kosaki, and Marika all knew each other, as reported by the just-slightly-older Yui. (Tsugumi and Haru were there, too.) Chitoge and Kosaki are delighted to learn that they were "inseparable" friends back then -- it helps explain why they became such close friends so quickly in the present. But none of them except Marika seems to have recalled that time in more than the fuzziest way, which is why Raku isn't sure what the childhood promise was about or with whom.
Gender Blender Name: "Seishirou" is an explicitly masculine name. Seishirou Tsugumi is a Bifauxnen whose (unofficial) adoptive father didn't bother checking the child's gender ten years or so ago -- he just looked up Japanese male names and gave her one. In all that time, he still hasn't figured it out, although she's grown beautiful enough that the Distant Finale shows she's become a fashion model.
Genre Savvy: Shuu Maiko and Ruri Miyamoto
Gratuitous Polish: The childhood promise Raku and Chitoge recalls includes a Polish word -- "Zawsze," meaning "forever," "eternally," "always," something like that -- despite none of the characters being identified as Polish.
Hidden Depths: Ruri has a very emotional moment when she tearfully tells her great-grandfather of all the friends she's developed -- Kosaki, Chitoge, Seishirou, Marika (sort of), Raku ... she even includes Shuu, "I guess." Listening outside the door, Shuu shows an uncharacteristically gentle smile....
- Shuu also admits, much later, that he admires Raku for his Samaritan Syndrome and wants to be more like him.
I Didn't Mean to Turn You On: Haru is struggling against the crush she has on Raku. Then, as she and her friend Fuu drop by Raku's place, it comes out that she has a particular liking for traditionally Japanese themes -- such as his house's architecture. And just after that's mentioned, Raku comes to the door ... in the yukata which, he explains, he typically wears at home. She doesn't quite develop a Nosebleed.
I Never Said It Was Vanilla: Haru reminisces about a guy whose face she never saw (he was wearing a teddy bear costume as part of a School Festival) who, when she got lost at the festival, bought her ice cream and helped her find Kosaki. After she describes this, it occurs to her that it might have been Raku, but he denies it: "I didn't buy you vanilla ice cream!" And she realizes....
Lonely Rich Kid
Memento MacGuffin: The pendant Raku carries is not only a memento of his first love but also the only clue he has of her identity.
- Onodera and Chitoge also carry around a key as a memento of a promise ten years ago. Sounds awfully familiar...
New Transfer Student: Chitoge transfers into Raku's class in chapter 1. She's transferred schools a lot before because of her dad's travels.
- Later Seishiro Tsugumi
  - And still later, Marika Tachibana
  - And Paula McCoy
Not So Different: At first Chitoge and Raku seem to be polar opposites, but eventually they find out that they have surpassingly similar experiences as heirs of crime syndicates.
Real Men Cook: Raku is an excellent cook -- having to take care of his Yakuza family turned out to be a good training.
- The girls, on the other hand, or anyway Kosaki and Chitoge, are lethal chefs.
Shipper on Deck: Dear gods, there are so many. Ruri in particular physically shoves Kosaki together with Raku ("Oh centrifugal force! Can't help it!"), and has more than once told Kosaki to "rape" him. Claude is about the only member of the criminal gangs who doesn't support Raku-Chitoge. He's shown a number of signs implying Bodyguard Crush....
- And then there's Kosaki's little sister Haru, who supports Kosaki-Raku despite having a crush on Raku herself, and her friend Fuu who's pushing Haru-Raku although she may herself have feelings of (or beyond) Romantic Two-Girl Friendship for Haru. And Tsugumi's friend Paula is a Tsugumi-Raku shipper....
Troperiffic: Think of a Romantic Comedy trope. There's good chance that it applies.
Tsundere: Ruri has a bit of this, but only toward Shuu. On one occasion, after he'd loudly admired the other girls' appearance but was more casual about hers, she hit him with what the narrative text called an "I-don't-really-care-but-I'm-still-kind-of-pissed-off-punch."
Twice Shy: Raku and Kosaki.
Unprovoked Pervert Payback: Averted. Chitoge finds Raku in the women's side of the hot spring, but she quickly figures that it's because Claude switched the signs to destroy Raku's reputation.
- Played straight whenever Tsugumi is involved.
Wham Chapter: Chapter 13 in which Chitoge remembers that she once made a promise with a boy. A promise that is word for word identical with the one Raku made.
What an Idiot!: Claude raised Tsugumi from early childhood. In some ten years he hasn't figured out she's a pretty girl, not a handsome boy.
Yakuza
Zettai Ryouiki: Chitoge sports impressive Rank A one.