RinLen

RinLen is the het ship between Kagamine Rin and Kagamine Len from the Vocaloid and Project SEKAI fandoms.

Canon
Kagamine Rin & Len do not have an official relationship, and this has been confirmed in 2020 by Cryptonloid developer Wataru Sasaki on Twitter. Ever since their release, the mirror images have been used in many songs that potray them in a romantic context. The two most popular ways they are portrayed is as siblings or as a couple. It is worth mentioning that there are songs that also portray them as rivals or just as friends. However, none of the songs that are produced for these two should be considered canon, as VOCALOIDs and other vocal synths are meant to be creative outlets for the producers, fans, etc. that use them.

RinLen Sibling/Family songs
Giga-P and Reol's song is a great example of a song about sibling rivalry. The song is about Rin and Len making stupid and silly competitions. In the end they just continue arguing. Another good example of a song portraying them as siblings is by Dixie Flatline. This song is about them rekindling after an argument. Other songs include:
 * synchronocity by Hitoshizuku-P
 * Servant of Evil by mothy
 * by mothy
 * Childish war by giga-P

RinLen Romantic songs
HoneyWorks' song is a great example of a song showing Rin and Len in a romantic way. The song is about Len trying to win over Rin but is failing miserably because Rin does not know how to accept his feelings. At the end of the song, Rin finally comes to terms with her feelings and accepts Len's confession. Other songs that include them in a romantic way are:


 * by Halyosy
 * by Wakacha
 * by Ningen Dokku
 * by TeamOS
 * by Hitoshizuku-P
 * Remote Control (in the Novel) by WONDERFUL★OPPORTUNITY!
 * Juvenile by Dixie Flatline
 * Chocolate box by Dezzy
 * Rin Rin Signal by Signal-P
 * At the ruins of atalieresta by Cosmo@Bousou-P
 * Karakuri卍Burst by Hitoshizuku-P
 * Re:birth by Hitoshizuku-P
 * Suki Kirai/Love-Hate by honeyworks
 * Meloncholic by Junky
 * Kimipedia by Junky
 * Why don't you call me yet by liveP
 * Haitoku no Hana/corrupted flower by Hitoshizuku-P
 * prisoner/paper plane series by Shūjin-P
 * PROMISE∞RING by Lettuce-P
 * The Wolf who Fell in Love with Little Red Riding Hood by Hitoshizuku-P
 * Nazotoki/Nazokake by Hinata Haruhana
 * Knife by Rerulili
 * Where shall we go? by Mellowcle
 * Electric Angel (Giga-P Remix) by Yasuo-P

Project SEKAI
In Project SEKAI, the Rin and Len's relationship differs in each unit's SEKAIs, although they are generally on good terms. Their relationship is most defined in the Street SEKAI, where they, despite often bickering, regard each other as partners and are important to each other.

Fanon
Although RinLen is considered one of the most famous Vocaloid ships, supported by many fans of the characters and which is associated with them in many ways, a noticeable number of people also view it rather negatively, given Crypton's Scrapped concept/idea positioning of the characters as twins. leaving as their "official" concept only the statement about the mirrorness of the characters. Alongside this, it's already a common misconception that Rin and Len are canonical twins. The argumenting over the ship has gotten so bad in certain circles to the point where even the official Project SEKAI English Discord server banned the topic, due to "the server not containing the maturity needed to have conversations like this."

Because of this misconception, it often creates tensions between fans and typically leads to flamewars online, to the point people spread misinformation for the Kagamines being "originally twins" as it was never the case stated by Wataru Sasaki on X/Twitter.

The headcanons of being twins, friends, lovers or in any case are all popular in their own ways, their relationship in semi-official media such as Sega in Project Diva and Project Sekai have always been deemed ambiguous for the fans for them to personally view whatever relationship they think they have in their own viewpoints and ways

One way or another, regardless of the portrayal of twins or lovers (or even both), RinLen is still one of the most popular in the franchise and for Rin and Len, due to the fact that they are the very first and famous "twin pair" Vocaloid project. It not only is the most popular Vocaloid ship in AO3, but also the most popular ship in most of the fandom related pages.

Fandom
FAN FICTION

Trivia

 * Another fanon headcanon describes Rin and Len as mirror images of the same person, some songs also describe them as genderbent versions of the same person. For example, one of MikuRin's songs is about how Rin turns into Len in order to get a chance for a relationship with Hatsune Miku.
 * Considering how often the relationship between these two inspires producers to write dramatic and tragic stories, there is a joke in the fandom that any song with their participation will contain dark and evil elements (especially featuring Len dying).
 * There are also songs that portray Rin and Len as both a couple and as siblings. One of the most famous songs that portray them in this way, would be the parody song of Cendrillon, Adolescence by Signal P, Though their relationship in Adolescene has been deemed ambiguous meaning it could mean anything, ranging from siblings in love, kids refusing to grow up, a knight and princess situation, young non-related love, or kids getting seperated due to getting old and hitting puberty or anything etc etc...
 * Their Kizuna Rank titles are: "Kagamine Duo", "Always Together" and "Heated Up".
 * In Project SEKAI, they have an alternative duet version of "Ghost Rule", "Bug" and "Torinoko City".
 * Len also has an alternative vocal for "Lost One no Goukoku", which features Rin as the original singer. Meanwhile, Rin also has an alternative vocal for "Kagirinaku Haiiro e", which features Len as the original singer
 * One of Asami Shimoda's (the Kagamine's own voice provider) favorite songs of Rin and Len is a love song between them that being Rin Rin Signal by Signal-P all stated in an interview also mentioning all different forms of relationship concepts ideas to be made and given to the fans

Variations

 * Big 8 refers to the ship between the two, Hatsune Miku, Megurine Luka, KAITO, MEIKO, GUMI and Kamui Gakupo
 * Cryptonloid Gang refers to the ship between the two, Hatsune Miku, Megurine Luka, KAITO, and MEIKO
 * CV Series refers to the ship between the two, Hatsune Miku and Megurine Luka
 * Kagumine refers to the ship between the two and GUMI
 * KaiRinLen refers to the ship between the two and KAITO
 * RinKuLen refers to the ship between the two and Hatsune Miku