Big 8

Big 8 is the poly ship between MEIKO, KAITO, Hatsune Miku, Kagamine Rin, Kagmine Len, Kamui Gakupo, Megurine Luka and GUMI from the Vocaloid fandom.

Canon
The eight characters belong to the voice synthesizer Vocaloid. Miku, Rin, Len, Luka, MEIKO and KAITO are all from Crypton Future Media, and appear in many semi-official stuff together. Meanwhile, Gakupo and GUMI belong to another company, Internet Co.. Because of this, The eight don't appear all together commonly. However, there's been some media where Gakupo or GUMI have appeared alongside Crypton Vocaloids. For example, Gakupo appeared in the manga Hatsune Mix, and GUMI appeared in the game Project MIRAI. There's still not official relationships between them, not even between the six Cryton Vocaloids. Their relationships, dynamics and status can varied depending on the song that they sing together.

Songs
The NighT ∞ Series revelves around a play called "Crazy ∞ Night", performed by the eight characters. In the song 'BaD ∞ EnD ∞ NighT'' Miku, who plays a villager girl, sheltered in a mansion. The masion is inhabited by the Head of the House (KAITO), his wife (MEIKO), his daugther (Luka), a doll boy and girl (Len & Rin), the butler (Gakupo) and the maid (GUMI). Later, Miku discovers a room full of coffins, and because of this, she tries to found the key in order to escape from the mansion. She realized that the "key" is murdering all of them, so she takes the clock's hands and use them to kill everyone there.

In CrazY ∞ NighT the play start over from scratch. After the Crazy Night party, the owners of the house realized that the clock stopped at three minutes until midnight and Miku had disappeared and the next page of the script was torn out. The page is nowhere, so they came to the conclusion that Miku most likely stole it. Miku apperas again and, like in the previous song, kills everyone with the clock hands. But then the others tell Miku that it is not the "True End", and it is very late for her to found it now.

In TwilighT ∞ Nigh, like the previus song, a page of the script is missing. When Miku was going to kill everyone again, the missing page appeared inside a letter that Miku had. However, the page was dyed badly, so the true end couldn't happen.

In EveR∞ LastinG ∞ NighT, it turns out that everyone is stuck in their roles and Miku is the only one who knows that everything is a play. When Miku was trying to save everyone, she listen them talking about "bring the real girl from the grave and switch her with the fake one", making her realize that she was someone's sustitution. Instead of taking the clock hands again, she runs to the coffins room and writes with her blood in a letter "The Everlasting Night has fading away, here comes a new dawn". The others reach the room and Miku uses the clock hands to kill herself instead of the others, so everyone returns to the reality.

Fanon
Miku, Rin, Len, Luka, KAITO, MEIKO, Gakupo and GUMI were the 8 first Vocaloids to reach high levels of popularity. Until IA came out in 2012, there were by far the most popular Vocaloids. Because of this, they are a very iconic group within the fandom. There have been multiple fan arts, songs and headcanons of the eights. Some fans like to add a 9th or 10th member to the group, such Miki, Lily, Piko, IA, MAYU, Flower, Fukase, etc.

Despite of all, the Big 8 is criticized by some people how believe that they overshadow all the other Vocaloids, for how fans are mostly focused in the same eight characters and ignore the rest. In the eastern fandom, the Big 8 have lost popularity because of the popularity increase of Vocaloids like IA, Yukari, Flower, Una or even KAFU (who isn't Vocaloid) and the decline of some like Gakupo. Meanwhile in the western fandom they are still widely popular and the favorite Vocaloids of most of fans, specially because of the nostalgic vibes that they give.

In terms of shipping, most of the ships that involve them are pretty or very popular, being some of the most popular ships between the fandom. Some people also likes to group the in 4 separated ships.

Trivia

 * Despite not being the first Vocaloids, they are the eight first japanese Vocaloids.