Not necessarily full discographies but enough to have an opinion on.

• 1000nichi-go no Hanashi.
• 2_wEi
• 22/7
• 3B junior and sub-units
• 7 Princess
• 7HOUSE
• 80_pan (formerly Harenchi☆Punch)
• 9nine
• a・chi-a・chi
• AAA
• ABCHO
• Abe Asami
• Abe Natsumi
• adieu
• AeLL.
• Afilia Saga (formerly Afilia Saga East & Junjou no Afilia)
• After School (Korean discography)
• Agnes Chan
• Aice5
• aiko
• Air (game/anime) songs
• Aiurabu
• AKB48 up until like 2017 or so
  • AKB48 stage songs
  • AKB48 Team Surprise
  • AKBIdoling!!!
  • Chocolove
  • DiVA
  • French Kiss
  • Honegumi
  • NO NAME (AKB0048)
  • no3b
  • Not yet
  • Watarirouka Hashiritai 7 (formerly Watarirouka Hashiritai)
• AKINO from bless4/AKINO with bless4
• AKIRA (model)
• ALI PROJECT
• amorecarina
• AMOYAMO
• Amuro Namie kinda sorta
• Angel Beats! songs
• Angela Aki
• Angela Zhang kinda sorta
• angela
• Angelababy
• ANGERME (formerly S/mileage)
• Ansatsu Kyoushitsu songs
• ANZA
• Aqours and other Love Live! Sunshine!! artists
  • AZALEA
  • CYaRon!
  • Guilty Kiss
• aquanote (Japanese idol group)
• Arashi kinda sorta
• Artery Vein
• Asami Rin
• Ashida Mana
• AsoBit Girls
• Asou Natsuko
• Athena & Robikerots
• AVAM
• AXIA
• ayaka's early stuff
• Ayana (I've)
• Ayano Mashiro
• Azumanga Daioh songs
• azusa (Mitsu Azusa)
• B-PROJECT kinda sorta
• B'z kinda sorta
• BaBe
• Baby V.O.X
  • Baby V.O.X ReV
• BABYMETAL's early stuff
• Bakemonogatari songs (first season only)
• Bakusute Sotokanda Icchoume and sub-units
• Be-ppin
• BELLRING Shoujo Heart
  • THERE THERE THERES
• Berryz Koubou
• BETTA FLASH
• Bety
• BEYOOOOONDS
  • Ame no Mori Kawa Umi
  • CHICA#TETSU
  • SeasoningS
• bijous
• Bishoujo Club 21
• Bishoujo Senshi Sailor Moon songs (original anime & live action)
• Bitter & Sweet
• Blueberry Girls
• BoA (mostly Japanese discography)
• BON-BON BLANCO
• BOYSTYLE
• Brown Eyed Girls (Korean discography)
• BsGirls
• bump.y
• Buono!
• Buzy
• C-ute (℃-ute)
• Canary Club
• Candies
• Candy Mafia
• Candy zoo
  • Candy zoo Nightmare
• Cardcaptor Sakura (original anime) songs
• Cha'R
• Chata
• CHECKICCO and related
  • CHEE'S
• Cheeky Parade
• Cheer song project
• Cherrybelle
• Chrome Shelled
• Chu-Z (also Chaos Underground Zealot)
• Chun Sang Ji Hee The Grace
• Ciao Bella Cinquetti (formerly THE Possible)
• Clannad (game/anime) songs
• ClariS
• CLOVER (seiyuu unit)
• CoCo (Japanese idol group)
• Coconuts Musume
• COLORS (Kitahara Sayaka unit)
• CooRie
• Country Girls
• Country Musume
  • Country Musume ni Ishikawa Rika (Morning Musume)
  • Country Musume ni Konno to Fujimoto (Morning Musume)
• Crush Tears
• Crystal Kay
• Cutie Pai
• CUTIE STREET
• CYNHN
• Cyntia
• D-LOOP
• Da Xiao Jie
• Daisy x Daisy
• Danceroid
• Dancing Dolls
• Deep White
• deeps (also dps)
• dela
• Dempagumi.inc
• denk!girls
• Diana Garnet
• DIANNA☆SWEET
• Do As Infinity
• DOLL$BOXX
• Dorothy Little Happy
• dot hack//sign (.hack//sign) songs
• Dream
• Dream Morning Musume
• Dream5
• E-girls
• Ebisu Muscats (original incarnation)
• EE JUMP
• Equal Love (=LOVE)
• Excel Girls
• f(x) (Korean discography)
• Fairies
• Falench.
• Faylan
• FictionJunction and related
  • FictionJunction YUUKA
• Flower Notes
• Free! (gay swimming anime) songs
• fripSide
  • fripSide NAO project
• Fudanjuku
  • Nakano Fujo Sisters
• Fujimoto Miki
• Fukuda Asuka
• FuwaFuwa
• Gacharic Spin
• Galaxy Angel songs (anime & game)
• GAM
• GCiB (Girls Crying in Bathroom)
• GEM (Japanese idol group)
• Girls' Generation (Korean discography)
• globe
• Gokujou!! Mecha Mote Iinchou songs
• Goriki Ayame
• Gotou Maki
• Gran☆Ciel
• GRANRODEO
• Guardians 4
• Gunjou no Sekai
• Haibane Renmei songs
• Haiyoru! Nyaruko-san songs
• Hajime Chitose
• Hamasaki Ayumi's older stuff
• hana*hana
• Hanamaru Youchien songs
• Hanazawa Kae
• Hanazawa Kana
• HANGRY & ANGRY-f (formerly hANGRY & ANGRY)
• Haraeki Stage A
• Haruna Ai
  • ♥♥♥LOVE♥♥♥
• Hashimoto Kanna
• Hauptharmonie
• Hayami Show
• Hayashi Asuca
• Hayashibara Megumi
• Hayate no Gotoku! songs
• Heike Michiyo (post-H!P as Michiyo)
• Hello! Project (everything else; can't be bothered listing them all but I've listened to every H!P shuffle/one-shot/special unit)
• Hello! Project Kenshuusei
  • Hello! Project Kenshuusei Hokkaidou
• Hetalia songs
• Hexagon All Stars stuff that Satoda Mai participated in
• Hey! Say! JUMP's early stuff
• Hibari Misora
• Higurashi no Naku Koro ni (original game/2006 anime) songs
• Hinagata Akiko
• Hinatazaka46
• Hinoi Team
• Hirano Aya
• Hisakawa Aya
• Honda Mari
• Horie Yui
• Hoshino Michiru
• Hyadain
• i☆Ris
• Ice Creamusume
• Ichigo Marshmallow songs
• Ichii Sayaka
  • Ichii Sayaka in CUBIC-CROSS
• ICHIKO
• Idol College
• IDOL Street Street-sei and related
• Idoling!!! and related
  • ChocoLe
• IDOLiSH7 kinda sorta
  • MEZZO''
• Iida Kaori
• IKU (I've)
• Inaba Atsuko
• Inoue Marina
• Ishida Youko
• Ishihara Kaori's early stuff
• Ishii Rika (formerly Peachy)
• Ishikawa Chiaki
• Itano Tomomi
• Itou Eri
• Itou Kanako
• JAM Project
• Jewel☆Rouge
• Jia Jia
• JKT48's early stuff
• Juice=Juice
  • NEXT YOU
• JUNNA
• Junsui Coffee Latte
• jyujyu
• K-On! songs
• Kago Ai
• Kalafina
• KALMIA
• Kamen Rider Girls
• Kami nomi zo Shiru Sekai songs
• Kanbe Miyuki
• Kandy Wong
• KARA (Korean discography)
• Karen (NICE GIRL! Project)
• Kasai Tomomi
• Kawada Mami
• Kawano Marina
• Kayou Aiko
• Kikkawa You's early stuff
• Kiniro Mosaic songs
• Kinniku Shoujotai
• Kirameki☆Unforent
• Kirarin☆Revolution songs
• Kishimoto Yumeno
• KissBee
  • KissBeeWest
• Kitahara Sayaka
• Kobayashi Azusa
• Kobayashi Yuu
• Kobushi Factory
• Koda Kumi
• Kominato Miwa
• Komine Lisa
• KOTOKO
• Kugimiya Rie
• Kuribayashi Minami
• Kuriyama Chiaki
• Kuroko no Basket songs
• Kurosaki Maon
• Larval Stage Planning
• Last Idol and sub-units
• Lia
• Lilpri
• Linda 3sei
• Linked Horizon
• Linlin
• LISP (seiyuu unit)
• Little Glee Monster
• Little Viking
• Love Hina songs
• LoVendoR
• Lucky☆Star songs
• Luna Amour
• LUNETTA
• Maeda Ai (actor)
• Maeda Irori
• Maeda Yuki
• Mahou Sensei Negima! songs (includes all anime adaptations & live action songs)
• Mahou Shoujo Madoka Magica songs
• Mai-HiME songs
• Maison book girl
• MAKO (I've)
• Mano Erina
• Marble Angel
• marriage blue
• Mary Angel
• Mary Doll
• Masuyama Kayano
• Matsumoto Kanae
• Matsuura Aya
• Meada Atsuko
• meg rock
• MELL (I've)
• Melocure
• Melon Kinenbi
• Mia REGINA
• Mika Todd
• Milky Holmes
• Miyamoto Karin
• Miyoshi Chinatsu (later Chigi Rumiko)
• Moe x Kon
• MOMO (I've)
• Momoi Haruko
• Momoiro Clover Z (formerly Momoiro Clover)
• Momomomo Paradise
• Morning Musume and sub-units
  • Minimoni and Minihams
  • Morning Musume 20th
  • Morning Musume Sakuragumi & Otomegumi
  • Morning Musume Tanjou 10shuunen Kinentai
  • Petitmoni
  • Tanpopo
• MOSAIC.WAV
• Muse (μ's) and other Love Live! School Idol Project artists
• Nakazawa Yuuko
• nano.RIPE
• nao (anison singer)
• Nijigasaki Gakuen School Idol Doukoukai and other Love Live! Nijigasaki School Idol-bu artists kinda sorta
• Nishino Kana
• NMB48 up until 2015
• Nogizaka46
• Nomizu Iori
• Noto Arisa
• Ogata Megumi
• Ogata Risa
• Ogawa Mana
• Ogura Yui's early stuff
• Oha Girl maple
• Oku Manami (as Ogu Manami)
• OLDCODEX
• Ongaku Gatas
• Ono Daisuke
• Ono Erena
• Ono Kenshou
• Onyanko Club and sub-units
  • Nyangilas
  • Ushiroyubi Hikaretai
  • Ushiroyubi Sasaregumi
• Ootani Masae
• Ootsuka Ai
• Orange Caramel
• Oranges & Lemons
• OS☆U
• Osaka Performance Doll
• Pabo
• PAPAYA
• PASSPO☆
• Perfume (Japanese idol trio)
• Petit Milady
• Petit Passpo☆
• Philosophy no Dance
• Pierre
• Pile
• PIPO☆Angel's
• Poetreep
• predia
• Priest (Kominato siblings)
• Prizmmy☆
  • Prism☆Box & Prism Mates
• PURETTY
• RABBIT HUTCH
• Ranaqura
• Rev.from DVL
• Rie fu
• Rin (Suenaga Mami)
• RINA (I've)
• Riot Baby
• RO-KYU-BU!
• RO-KYU-BU!
• ROSARIO+CROSS
• Rosy Chronicle
• ROUND TABLE featuring Nino
• route0
• RYUTist
• Sakamoto Maaya
• Sakura Gakuin and sub-units
• Sakura Maya
• SAKURA*TRICK
• Sakurakko Club Sakuragumi
• Sashihara Rino
• Satohaka Aya
• Sayonara Zetsubou Sensei songs
• Sayubee (Takagi Sayuki)
• SCREEN mode kinda sorta
• SDN48
• See-Saw
• Sharam Q
• Sheki-Dol
• Shibata Ayumi
• Shibuya Azuki
• SHIHO (I've)
• Shikata Akiko
• Shimamiya Eiko
• Shimatani Hitomi
• Shimokawa Mikuni
• Shingeki no Kyojin songs
• Shinseiki Evangelion songs
• Shinvi
• Shiritsu Ebisu Chuugaku
  • that band they did
• Shoujo Byou
• Shugo Chara Egg!
• Sister Q
• SKE48 up until 2015
• SNH48's early stuff
• SNoW
• SO.ON project
• Sonim
• Sonoda Anna
• Sora no Otoshimono songs
• Sparking☆Point
• SPEED
• Sphere (seiyuu unit)
• spirit color (stylised as (s)pirit color)
• Splash! (STUDIO HIP'S girl group)
• Starbow
• Starmyu songs
• StylipS
  • Team DEKARIS (StylipS before StylipS existed)
• Sunday Girls
• SUPER☆GiRLS up until about 2015
• Suzumiya Haruhi no Yuuutsu songs (does not include Nagato Yuki-chan)
• SweetS
• Sweety (KPop co-ed kids group)
• T-ARA (Korean discography)
• Taiyou to Ciscomoon (also T&C Bomber)
• Taiyou to Odore Tsukiyo ni Utae
  • Taiyou to Odore
  • Tsukiyo ni Utae
• Takagaki Ayahi
• Takeuchi Akari
• Tamai Shiori
• Tamura Meimi
• Tamura Yukari
• Tanaka Rie
• Tasaki Asahi
• Team Syachihoko (not so much TEAM SHACHI)
• THE iDOLM@STER (original)
• THE iDOLM@STER Cinderella Girls
• THE iDOLM@STER SideM
• THE ME
• TnyGinA
• To Aru Majutsu no Index songs
• Tokimeki Sendenbu (not so much Chou Tokimeki Sendenbu)
• Tokitou aMi
• Tokyo 7th Sisters artists
• TOKYO GIRLS' STYLE
• Tokyo Mew Mew (original) songs
• Tokyo Performance Doll (original)
• Tomita Maho
• Tommy heavenly 6
  • Tommy february 6
• Toradora! songs
• Tottoko Hamtarou songs
• TrySail
• Tsubaki Factory
• Tsuji Nozomi
• Tsunku
• twinklestars
• ULTRA-PRISM
• Umeda Erika
• Umineko no Naku Koro ni (game & anime) songs
• Under17
• Up Up Girls (Kakko Kari)
• Up Up Girls (Kakko Niki)
• Utatsuki Kaori
• v-u-den
• W (Hello! Project)
• Wake Up, Girls!
• Watanabe Mayu
• Weather Girls
• Weird Al Yankovic (lol)
• Wink kinda sorta
• Wonder Girls (Korean discography)
• wyenra
• Yajima Maimi
• Yamaguchi Momoe
• Yamato Nadeshiko (seiyuu unit)
• Yes Happy!
• Yokoyama Rurika
• You'll Melt More! up until Younapi left
• Younapi
• Yousei Teikoku
• yozuca*
• YuiKaori
• YUKA (Kiddy Grade artist)
• Yuuki Aira
• Yuuki Aoi
• YUZUNO (I've)
• ZARD