The term "Derivative" is used here to describe a fanmade Vocaloid character that is based on an already existing character.
Haku was originally made as a representation of songs that use Hatsune Miku but ended up sounding awful. In such cases, the makers of that music would then proceed to whine about how their work never received attention and later moved on to whine when criticism stated their work as dull and boring, or was posted quite late when few people were on Nico Nico Douga. She became popular and her creator Caffein later established other characters following the same procedures, each representing a different aspect of failure within the Vocaloids.
Haku is one of the derivatives of Vocaloids that became officially recognized by Crypton Future Media, the publisher of the Character Vocal Series for Vocaloid2. The other derivatives bearing this distinction is Miku Hachune, Neru Akita, Meiko Sakine, and Tako Luka.
Because of her popularity, merchandise of Haku appear alongside official Vocaloids.
Official licensed Haku figurines have been produced: a Nendoroid Puchi, a scale model and a plush.
In Maker Hikōshiki Hatsune Mix, Haku makes a cameo appearance as a student of Neru (ch6) and is also in chapter 7 and chapter 14, then she later appears drinking sake with Meiko (ch16).
In the Project DIVA series, Haku is an available character in the PSP game, -Project DIVA- and again as a playable character in its sequels. If the player has not chosen her for a long time, she is complete with moody mannerisms.
- Haku was originally marked as badly-done Miku Hatsune songs which were uploaded onto NND. However some have tried to give her an actual voice using Miku's voice and manipulating it to sound depressed, through methods like down pitching her. These were later also switched to the Miku Appends as some such as Miku Append Dark produced the desired results much easier.
Another suggests a manipulation of MEIKO's voicebank to produce Haku's voice.
It has been pointed out by some fans, when speaking about songs and PVs that feature Haku singing, say that if one succeeds at producing a "bad" song, then no failure was met in the process. There are a small number of fans who disapprove of such songs, this is because it can be considered a contradiction to the point of Haku's existence being based on failure. This in particular is also aimed at the Haku songs that end up sounding "good" as Haku was meant to be far from this ideal. However, whatever songs that come out in her name are subject to the interpretation of the producer, whether they follow Haku's depiction of failure or not.
- Haku is referred to as a "VOYAKILOID". In Japanese, "Boyaku" (ぼやく) means grouchy or to grumble and complain, the pronunciation in Japanese is Boyakiroido.
- Going by Caffein's character sheet commentary, Haku's early design had a tinge of grey skin, but it was not well received. Her red eyes were not an attempt to reflect albinism but merely inspired while watching a Ghost in the Shell: S.A.C. music video on Nico Nico Douga. The character in the video, Motoko Kusanagi, has red eyes.
- While she was conceptualized to originally be a Miku user, Caffein states it is not a problem to think of her as a failing Vocaloid, or a co-worker, or the lady at the small candy shop, etc.