|Spoiler warning: this article may contain major plot or ending details.|
"The Promise Girl" refers to the identity of the young girl that Raku hung out with on the Tenku Plateau, they then made a promise of marriage the next time they met by exchanging a set of lock and key.
Before the true identity of the promise girl was revealed in the end of the series, fans have long speculated and produced legitimate theories on her identity.
This was the theory that held the most ground until, finally it was canonly disproven.
Clues found by fans include-
- According to both the anime and the manga, Raku dreams of a girl with long hair. Only Chitoge's younger version is revealed to have long hair along with Yui . However, Yui herself denied she was the promise girl in the manga.
- Kosaki's story book "Zawsze in Love" was not bought by her mother but given to her. Assuming that the girl Raku changed the story for was the promise girl, Kosaki did not receive the book until the story was changed. Hence, the true holder of the book, Chitoge, must be the promise girl.
- The anime, in its ending theme, showed the girl reading the book a red ribbon and was blonde. Chitoge was the only girl who had such features.
- Out of all the girls, only Chitoge remembers the phrase "Zawsze in Love".
The probability of Marika being the promise girl was minute if not non-existent. Nevertheless, fans saw some ways it could be possible-
- The fact that no clues point towards Marika is a clue in itself that she is the promise girl. It is a scheme of the mangaka to divert the attention from Marika towards Chitoge and Kosaki and give a surprise ending.
- The photograph of Raku and Marika, each holding the lock and key respectively as kids was the evidence of Marika being the promise girl.
- Marika seems to be hiding something when the storybook comes into focus. It could be fact that she is the promise girl herself but keeps it hidden for she doesn't want Raku's feelings from ten years ago to affect his volition now. Moreover, Raku had amnesia during this arc.
- The promise of marriage made with the promise girl as Raku keeps seeing in his dream comes closest to Marika remembering her father making a deal with Raku's father to not arrest his Yakuza clan in exchange of Raku and Marika's marriage in the future.
After Yui denying it herself that she wasn't the promise girl, speculations surrounding her quickly faded. However, two pictorial evidences are still popular among fans.
Yui was also thought to be denying her being the promise girl as she was rejected and didn't wish Raku to choose her just because of some childish promise they made together 10 years ago.
However, even though such restraint was typical of Yui's character, she had recently given up such thinking thanks to Night and Marika. It was highly unlikely that would go back to being a martyr.
Due to a lack of a promise key designated to Tsugumi's keeping, Tsugumi falls flat to any speculation of being the promised girl.
Fans assumed that Tsugumi's key would be later revealed as the fourth one, however Yui's introduction falsified this. Also, it wouldn't make sense that Tsugumi would remember a promise made by Chitoge ten years ago and not the one she made too at the same time at the same place.
Haru was assumed to be the promise girl just because (i) she turned out to be there too 10 years ago and (ii) she wanted the story book not Kosaki.
No other theory surrounds Haru.
- Nisekoi, chapter 221-226