Hatsune Miku Character Items
Vocaloid characters are often depicted with a particular item, for example Hatsune Miku is often pictured as holding a leek and Kagamine Rin a mikan orange. This is often a source of confusion for many people who are unfamiliar with Vocaloid characters as the relevance of these items is not immediately obvious.
The affiliation of Vocaloid characters with certain items has its roots with "Item Wars" (持ち物戦争, mochimono sensou) that occurred between fans online. Fans would depict their favorite Vocaloid in art or memes with a certain item, usually based off of their color scheme or assumed personality. These depictions grew in popularity, occasionally with differences in opinion on which item would suit each character best, the "Item Wars".
While not part of the original character design, most popular Vocaloids have a fan designated character item, many of which have become officially recognized by the original maker due to their immense popularity amongst fans. For example, while a leek was never part of Hatsune Miku's original character design, it is now not at all uncommon to see official illustrations and figures depicting her holding the white and green vegetable.
Hatsune Miku
Hatsune Miku's character item is commonly accepted to be the leek, a long, cylindrical, white and green vegetable. The origin of Hatsune Miku's association with leeks dates back to 2006, when the Loituma Girl (also known as "Leekspin") flash animation became a popular meme on the Internet. This flash animation depicts the Bleach anime character, Inoue Orihime, twirling a leek set to the traditional Finnish folk song "Ievan Polkka".
In 2007, a Vocaloid cover of "Ievan Polkka" was made, which was sung by Hatsune Miku and accompanied by an animation of Hatsune Miku waving a leek. This video was immensely popular, which along with Hatsune Miku's teal green color scheme, has resulted in Hatsune Miku often being depicted holding a leek. The leek has become Hatsune Miku's unofficial character item and fans may often be seen wielding both official and unofficial leek shaped goods, including glowsticks and occasionally even real leeks, at Hatsune Miku related events.
Kagamine Rin/Len
Kagamine Rin and Len's character items are commonly accepted to be the fruits mikan orange and banana respectively. Rin's yellow hair combined with her large white bow accessory is said to resemble a mikan orange with leaves attached, while Len's likewise yellow but unruly hair and is said to resemble a bunch of bananas.
The Kagamine twins do also have another shared character item, though they are not usually seen carrying it. In many fan artworks and videos, they are seen driving a road roller (similar to a steamroller) together, often to comedic effect. The origin of their affiliation with the road roller is said to be a fan video released in December 2007, after Kagamine Rin was announced but before the product was actually released. Road rollers are also associated with the JoJo's Bizarre Adventure character Dio Brando, who threw one as a weapon and who's unique battlecry is "WRYYY". Due to the fact that road rollers are also yellow and "WRYYY" sounds similar to "Rin", the video comically suggested that Rin's character item should be a road roller, an idea which caught on in popularity and is now officially recognized.
Megurine Luka
Megurine Luka has several character items, due to split opinions which lead to an intense item war. Before Luka's official release, the Vocaloid fan base had narrowed several potential character items for her, as usual, based on her color scheme and assumed personality. These included things such as whips, peaches, flamingoes, and wine, though the two most popular items were a frozen tuna and the Gluttony Sword from Final Fantasy XI.
In February 2009, less than a week after Megurine Luka's release, a video of Tako Luka (たこルカ, lit. Octopus Luka) singing PoPiPo was uploaded to Nico Nico Douga, which gained immense popularity due to its cuteness and ridiculousness. The popularity of this video and character brought an end to the feud between the frozen tune and Gluttony Sword factions and the Tako Luka meme eventually became Megurine Luka's character item/mascot.
Tako Luka is a derivative character was created by a fan who thought that Luka's hair resembled an octopus, and while not an "item" per se, Luka is often depicted together with Tako Luka and have been depicted in a Nendoroid figurine together. As octopi and tuna both share the common theme of being seafood items in Japan, the frozen tuna has also managed to remain on as one of Luka's character items, with Luka often being portrayed in comical situations using her frozen tuna as a weapon. It is also thought that another reason the frozen tuna remains as Luka's character item is that the Japanese word for "tuna" (maguro), sounds slightly similar to Luka's last name "Megurine".
KAITO
KAITO's character item is ice cream. He is often depicted holding a light blue ice cream bar, which is likely due to his blue and white color scheme. KAITO was originally believed to first have been depicted as an ice cream lover in a series of videos uploaded to Nico Nico Douga in September 2007.
Despite being released a year before, KAITO was not very popular at the time. In response to this, a fan released a video of Hatsune Miku singing the beginning of the song "you" from the Higurashi When They Cry game. In the video, Miku sings to KAITO "I wonder where you are and what you are doing right now," in an indirect comment from the video maker that due to KAITO's lack of popularity he had disappeared from the Internet, nowhere to be found. Another user made a joke video meant to be a reply from KAITO to Miku, singing back "Oh? I was actually just eating ice cream." This joke video led to a resurgence in KAITO's popularity and ever since, fans have agreed that KAITO loves ice cream, in particular, Häagen-Dazs, which is popular all across Japan.
MEIKO
While MEIKO has no official age, as one of the first Vocaloids to be released, MEIKO has the image of a slightly more mature woman in the Vocaloid family, especially compared to the younger Vocaloids who evidently have outfits based on school uniforms. This, combined with her more mature voicebank, lead fans to believe that MEIKO is at least of legal drinking age and that it, therefore, would not be unusual for her to enjoy drinking alcohol.
MEIKO is commonly depicted as enjoying Japanese sake, particularly the Ozeki One Cup. The origin of this meme is believed to be a song by One Cup-P, who had ordered Hatsune Miku at the time, but his delivery was delayed. In the song, he has MEIKO sing "everyone else is getting their Hatsune Miku delivery, but my delivery has been delayed, so I'm going to drown my sorrows by downing this One Cup in one go". While this was obviously One Cup-P's personal thoughts at the time, the fact that One Cup-P used MEIKO's voice for the video is thought to be a major reason for why MEIKO is now regarded by fans to like One Cups, sake and alcohol in general. While Ozeki One Cups are single portions of Japanese sake, fans have decided that MEIKO has a strong tolerance for alcohol and enjoys drinking large amounts, which is why she is now usually depicted with large bottles of Japanese sake instead of Ozeki One Cups.