The Z and the ZZ tags are special. The Z tag is for groups and assorted people who do not fit under another tag, and the ZZ tag is for series and other things that are not people.
This page may not be always up to date; sorry for the trouble.
Z tag explanations:Groups are made up of one or more people who are probably also tagged. If all of the people who are in a group are producers, the group will go under the P tag instead.
Z: R-square (RamuneP x Ryuusee)Currently people under the Z tag are people who only write lyrics, mix, master, or encode. And one person who has been specially thanked.
Z: ROZEO EMBLEM (Harry x Naoki Harashima x Koji Kunitomo)
I may eventually have to make new tags for these categories of people.
Z: 7@ (encode)
Z: Dakishimeta Tonight (lyricist, also utaite)
Z: Ishigantou (lyricist, also utaite)
Z: Issei Ambo (mix)
Z: Jota (lyricist and video...ist, also utaite)
Z: kaichi (mix and mastering)
Z: kigurumi (lyricist)
Z: Lasah (utaite)
Z: Maccha (mastering)
Z: Mary (lyricist)
Z: muu (lyricist)
Z: Nagi (mastering)
Z: Torii Hitsuji (lyricist)
Z: Yairesu (mix)
ZZ tag explanations:Series
ZZ: Heisei Project (Zips)Other
ZZ: Cool Reference Files (this song has a zip with things that an aspiring P might find useful)Tag ZZ: Hit Song easily gets outdated, my apologies.
ZZ: Debut Work (this song is the producer's first song)
ZZ: Double Post (This song has been posted twice by me- one post has additional lyrics)
ZZ: English Song (a song originally written in English)
ZZ: Hit Song (songs with 50k+ views and 5k+ mylists on the original upload)
ZZ: Karaoke-less (these songs currently lack karaoke)
ZZ: MMD PV (these songs have a PV made with MMD)
ZZ: Nico Nico Indies (these are non-vocaloid songs that were originally posted to nico)
ZZ: No Reprint Available (songs without reprints)
ZZ: Official VSQ (this song has a VSQ provided by the producer)
ZZ: Onaji Up (a producer and an utaite collaborated on this song and released a vocaloid and a utaite version simultaneously)
ZZ: UTAU (this song was originally sung by an UTAU)
ZZ: ♥ (Kitty's pimping tag= a select group of underrated songs that i think are super cool)