Chitoge doesn't directly remember Tenku Highland, but does get some deja vu from being there so walks around to jog her memory. Also the blurb for the volume and 'The story so far' introduction refer to it as Tenku Meadowland, but the rest of the manga doesn't, so I will still refer to it as Tenku Highland.
Raku is about to leave where Yui stops him to ask if he knows which one he likes. Raku does, so she asks if he wants to know what all those years but he declines. Yui asks Raku for his pendant and when he gives to her Night rushes around it to remove a broken piece of key that was stuck inside. Yui reveals that some of Raku friends from when he was younger tried to open it using Yui's key and he cried about for long time afterward. She kept secret that she knew everything because she knew she wasn't Raku's promise girl, but still wanted him to love her despite there being no 12 year promise between them. She sends him on his away.
Raku, Kosaki, Shu, and Ruri all arrive at Tenku Highland really early before dawn and as it's dark, decide to split into pairs : Kosaki and Raku, Shu and Ruri. Neither have a phone signal so can't call Chitoge, but Kosaki spots a figure in the distance which unfortunately turns out to be Claude. Raku sends Kosaki on ahead as he prepares to face Claude, who will not let him see Chitoge. Claude reveals he knew about Chitoge and Raku's fake relationship as well as the fact that Raku has eyes for another woman. Raku doesn't care for Claude's words and he going to see Chitoge come hell or high water, but luckily Seishiro appears in front of Raku.

Seishiro volunteers to fight in Raku's stead, allowing him to continue to search for Chitoge. Claude is appalled by Seishiro betrayal and attempts to convince her by explaining Chitoge's true reason for disappearing and this does convince Seishiro: convinces her that allowing Raku to see Chitoge is right thing as she cannot grow until she confronts her feelings. Claude disagrees as he believes Raku not to be worthy of Chitoge's affections, but Seishiro thinks he is and so they fight.
Raku is still searching when comes across and old abandoned building that he recognises as the building Marika stayed in 12 years ago. Marika para-glides in throwing herself at Raku. Marika reveals that she is up to speed with the whole situation (all thanks to Yui) and she also remembered everything from 12 years ago, but never said anything for the same reasons as Yui. She tries her key inside Raku's pendant and fails to open. She accepts that he in love with another woman (she hasn't given up on him) and tells him that Chitoge is at the top of a mountain. As hse leaves on a helicopter, Raku shouts that he was really glad that they became friends and Marika agrees with him.
Meanwhile Kosaki has stumbled on a place she recognises.

The place which Kosaki recognises is an old abandoned house, but she can't remember why recognises it, but does remember that one of the posts in the fence is loose enough that you lift it and create a gap to get inside. Kosaki remembers that this house was where Chitoge and her family lived and begins to relive memories as she explores the house. she wanders up to the first floor and finds Chitoge's room and remembers that she stored her picture book (Zawsze in Love) in the closet and opening said closet reveals the missing page of the book. This triggers old memories for her.
Meanwhile Chitoge has found a large rock that looks familiar, like you could see a little girl reading book on top of it. Chitoge further inspects the rock and discovers something that triggers old memories for her.
The old memories begin with Kosaki and Chitoge spending time with Marika in her room in the hospital when Yui swings on her way to visit her mother, who is also at the hospital. Yui reveals that she and Raku will be going home, as will Chitoge, because their fathers have made their agreement. Chitoge wants to meet with everyone again, so Yui suggests they make a promise which inspires Chitoge to make the promise like the one in the picture book as hse wants to marry Raku in the future.

Chitoge asks the most knowledgable person in the room, Yui, how to get a lock and key seen like in the book. However, Marika objects to such proposition, as Raku is her fiance and thus belongs to her. 5 year-old Chitoge doesn't understand what a fiance is, but does know that people have to be in love to get married and Raku hasn't said that he loves Marika, but neither has he said that loves Chitoge. Yui proposes compromise where a pendant-shaped lock is made, along with 4 keys as there are 4 of them and 4 keys in the story, also they all promise to meet up again in the future. Everyone agrees to the idea, but there is an issue regarding the key that actually opens the lock. This issue is still not resolved when the keys and pendant are made, so Marika and Chitoge force Raku to adjudicate like he is King Solomon the Wise. Unfortunately, Raku is 5 years old and not wise, so picks Chitoge to get the princess key as he like girls with long hair, rather than threatening to split in half. Later, Chitoge spots the final page from the Zawsze in Love book, which Kosaki has been whole time during this flashback, so sets out to return it to her. On her way over, she overhears Raku confess his feelings for Kosaki (if you were wondering why he chose Chitoge, that is because he didn't want admit that just likes Marika and Chitoge). Ever the honest man, Raku decides to tell Chitoge that he can't marry her, but Kosaki stops him so he doesn't her Chitoge's feelings and instead suggests they carve their names in a rock instead under a carving of an umbrella (this really romantic in Japanese culture). On the final day, Chitoge saves Raku the trouble by giving Kosaki the princess key, as they love each other and people in love have to marry the one they love. Chitoge asks Raku to promise that he takes good care of Kosaki and Marika demands that he promise to marry her, when the meet in the future. They all promise to meet up in the future (the entire point of all the locks and keys) and part ways, while Raku and Kosaki stay behind to promise to marry in the future using the pendant and the key.

Back at her home, Chitoge is packing up and finds the page she was supposed to give to Kosaki, but decides to leave it behind because what are odds that they are going to meet again.
Returning to the present, Kosaki in crying over how once again Chitoge has given up her chance to be with Raku so Kosaki can be with him, while Chitoge is crying because she wasn't Raku promise girl. Kosaki leaves the house to find Chitoge, because if one of them is going to get hurt, then the other should be with them to share the pain. However, Chitoge has now running away from the rock.
Claude and Seishiro are still fighting (physically and verbally) over whether not Raku should see Chitoge. Claude believes that Chitoge is too fragile (emotionally) to take rejection, while Seishiro is wholly convinced that Chitoge will get through the pain of being rejected. Claude throws 2 grenades at Seishiro, shooting one of them to make it explode while Seishiro throws the other one back. Claude catches and it doesn't explode which surprises Seishiro enough for Claude to pin her down however, Seishiro throws a combat chain around Claude's arm before looping it around a stick embedded in the ground (don't ask me where it came from), thus pinning Claude down as well as tying him up.

Claude is surprised at the move Seishiro pulled off and she reveals that while he wasn't watching, she grew and learnt new things so thus not the same person Claude assumed she was. Seishiro also remarks the same applies to Chitoge. Now that he has been defeated, Claude reveals a secret he had kept close to his heart: Seishiro should marry Chitoge as she is better husband material than Raku. Seishiro finally snaps and rips her shirt open to reveal her breasts (don't worry there isn't any nudity, she is wearing a bra). Claude assumes it is surgery and is swiftly corrected, but he still cannot believe that this fact was kept from him. Seishiro again corrects him and is disappointed that he never worked it out. Thoroughly beaten, Claude accepts defeat regarding the argument and the fight.
Ruri and Shu are still searching for Chitoge and Ruri asks Shu if he knows why Chitoge disappeared before revealing her own hypothesis. Ruri laments that if Raku and Kosaki got together earlier, then none of this would have happened. Shu is more at peace with the situation and argues that just because you have loved someone for a longer time doesn't qualify you to be more deserving of any reciprocation. Ruri takes this to mean that he is on Team Chitoge, but Shu corrects her as he is on Team love. Ruri once again asks if he still has feelings for Ms Kyoko and Shu finally gives answer which is yes. Ruri asks further if he ever did anything about and Shu tells her that he confessed his feelings with some assistance from Raku. Ruri remarks that she now knows what it is like to in Kosaki's shoes, as she now in love so Shu asks who the lucky fella is. Ruri reveals it to be him, confesses her feelings and states that she is willing to wait for him to be ready to love someone else. All this catches Shu off guard, which really pleases Ruri.
Meanwhile, Marika spots Chitoge running and drops down to speak with her.

Marika requests for Chitoge to return to the top of the mountain, as Raku will be arriving there anytime soon. Marika then asks if she is going to be doing he same thing she did as a 5 year-old. Chitoge confirms this by saying she is only going to get in Raku and Kosaki's way, so Marika calls her out on her cowardice towards the entire situation. Marika believes that the 2 proper options: 1: confess your feelings or 2: kept your feelings hidden but don't run away. Chitoge can't do any of those things as there no way she was going to win anyway. Marika asks how she came to know that the 2 liked each other and Chitoge reveals that she knew from accidentally eavesdropping on the 2 individually. Marika deduces that Chitoge doesn't know that she is one of the 2 people that Raku is in love with, so pleads with Chitoge to go back and face Raku. The convincing statement for Chitoge is that if she really loves Raku, then she should treat her love like it is nothing and so she runs back up the mountain.
Meanwhile, Raku is close to the summit just as dawn is about to break over Tenku Highland and in the morning glow he encounters Kosaki.

The 2 head up the mountain with Kosaki agonising over the fact that Raku doesn't know that Chitoge loves him. She asks him he knows why and the response is that he doesn't know exactly, but presumes it is something to do with him. He further elaborates that he knows when something is really on Chitoge's mind and he hates to see her struggle all alone. Kosaki then realises that Raku is in love with Chitoge and if she is going to confess her feelings then she should do so now. Kosaki confesses her feelings for Raku and the 2 begin to cry.

Raku confesses that he loves her as well, but Kosaki interrupts him and tells him that there is someone else who he loves even more, which he confirms. She hands him her key which he initially refuses, but accepts with the condition he is free to do whatever he likes with it. On his way to the summit, Raku opens his pendant and inside are 2 rings and 2 letters: 1 for older Kosaki and one for older Raku. 5 year-old Raku's letter to Kosaki talks about how he wants to live their future together, while 5 year-old Kosaki is more concerned if Raku will still love her. After recovering from the metaphorical gut punch delivered by his own guilt, Raku arrives at the mountain summit.

The 2 greet each other, although Chitoge refuses to face Raku. Raku is unsure what to ask, so Chitoge confesses her feelings for Raku and explains why she ran way and what information she learned that helped her makes this decision. Raku then tells her what happened between him and Kosaki on the way up to the summit before telling her that, while he was in love with Kosaki for a long time, he is now in love with someone else. This someone else is a person who is: a real troublemaker, always talks trash, clobbers him in front of classmates, always fought with him, and someone who he couldn't stand to begin with. However, as he got to this person, he realised that this person was actually sweet, kind-hearted, only appeared standoffish as she was just awkward, and now he loves this person. Raku apologises that he was also in love with Kosaki and that his indecision hurt Chitoge, but he has now made up his mind. Chitoge asks why her and Raku's response is that he is happy when with her. Chitoge still doesn't see it and lists all her flaws, but Raku still doubles down on his confession: he loves her, warts and all. Chitoge finally turns around and hugs Raku whilst screaming out her love for him and Raku responds with own declaration of love.

The 2 stop embracing and Raku asks Chitoge will return to school, but she declines and explains that whilst working for mother she didn't intend to go back to school, so starting looking for some job opportunities. A business friend of her mother is interested in her and has offered her a job, but she has take right away if she wants, which she does. The job requires a lot of travelling, so she won't be able to spend much time with Raku and could be away for up to a year, which Raku accepts. They return to the others and Chitoge and Kosaki are initially awkward towards each other, but once Kosaki begins to hug Chitoge, the tension between the 2 falls away like the tears from their eyes. Chitoge and Seishiro head to the USA to work for Hana, Marika returns to Pittsburgh, USA to continue her treatment and the rest return to Bonyari and finish their 3rd year of high school, with Raku managing to pass the university exams that he took (I cannot say for the others, but it is assumed that they too also passed).

Several years after the events of the last chapter, we are greeted to an older Raku Ichijo, who now works at Bonyari city hall in public safety, whilst also being the head of Shuei-Gumi Yakuza syndicate. His father is alive and well, as now spends his time travelling with his wife. Adelt has also stepped down from running the Beehive Gang and Claude is now the boss of that organisation, which has now found a permanent home in Bonyari. Today, all of the invitations for his and Chitoge's wedding have been delivered, so Raku calls Shu to make sure he and his girlfriend, Ruri, received theirs. Shu is a teacher and Ruri is a translator and are saving up for their own wedding. Ms Kyoko is also invited along with Haru and her friends. Haru now runs Japanese Confections Onodera and Fu is a journalist, who has written an article about Haru (and her family's Japanese sweet shop). Paula works in a lab as a researcher. Yui has also been invited and now pregnant, while Seishiro is model for Chitoge. Marika has completed her treatment and set to get married, once she finds a suitor who can hold candle to Raku (she is properly trying, honest). Kosaki is a cake decorator and her latest creation is a wedding cake for Raku and Chitoge.
Raku and Chitoge meet each other at the summit of Tenku Highland and Chitoge remarks that he is late. Raku quips back that he hasn't seen her in over a year because she is so busy as a world-famous fashion designer. Raku brings out a new pendant and key (they buried the old one under the large rock in the Highland), then Raku and Chitoge perform the promise ritual that he did with Kosaki when they were 5. The 2 lean into kiss each other (their first kiss ever) and sort of fail at it,not that we see it.
The bonus chapter involves Raku and Chitoge's son meeting Haru's niece, although we do not know who her parents are.

During my introduction for my review of volume 1 of this series, I posed the question that my opinion of Nisekoi could changed and I think it sort of has in that it has become more clearer. I think the series is alright, as it has its good moments and its has some good characters but equally the are moments where the series does make it difficult to like it and there are also a few characters who often ruin the scene that they are in more often than not. I think the series is a solid 7/10, as I feel like it deserves its long run but at the same time, it should not be considered a gold standard to which all shonen harem rom-com series should held against. The best advice I could give to someone wanting to pick up this series comes from my introduction for my review of volume 4: read the series if you like your rom-com to be more romance than comedy.