The first albums I heard?? let's see:

Ayu - i think it was RAINBOW
Namie - Style

My memory fails me but here we go...

Hikaru Utada: Exodus

L'arc~en~Ciel: SMILE

Crystal Kay: Best of Crystal Kay

Mika Nakashima: TRUE

Kumi Koda: Best~Second Session~

Ayumi Hamasaki: Duty

Namie Amuro: Past<Future

Utada - Deep River (and her best album too)
Koda - Secret

Ayu: love songs
Utada: ultra blue
Kumi: Universe
Angela aki: home
Perfume: JPN
Namie: best fiction

AKIHIDE - Amber

best album of 2013 , period

Well, let's see:
Aimer + fumika since their debut in 2011
Yui - I Loved Yesterday (2007)
KOKIA - Real World (2010)
Ayumi Hamasaki - Secret (2006)
Utada Hikaru - Ultra Blue (2006)
Kumi Koda - Japonesque (2012)
Namie Amuro - Uncontrolled (2012)
B'z - Action (2007)
Mika Nakashima - The End (2006)
...

Ayu: NEXT LEVEL
Koda Kumi: UNIVERSE
Namie Amuro: PAST<FUTURE
Utada Hikaru: First Love
Miliyah Kato: HEAVEN

Kumi Koda- Best~Second Session
Ayumi Hamasaki-(Miss)understood
Namie Amuro- Concentration 20
Gackt-Crescent(Turned out this was a boot. =( )

Ayu - missunderstood
Kuu - Black Cherry
Utada - Deep River
Maaya Sakamoto - Hotchpotch (her first best of)
Gackt - Diabolos
Namie Amuro - PLAY
Ai Otsuka - AI am best
BoA - best of SOUL
Tsukiko Amano - Catalog
Tommy Heaveny6 - Heavy Starry Heavenly
Ami Suzuki - Dolce
BIG BANG - ALIVE
miyavi - This iz the Japanese kabuki rock
UVERworld - Proglution
X JAPAN - Fan selection

A lot of best collections in there, lol.

Ayu: Secret
Kuu: Black Cherry
Namie: Play
Utada: Deep River
YUI: My Short Stories
Ayaka: Ayaka's History2006-2009
BoA: The Face
alan: Voice of Earth
Angela Aki: White
Anna Tsuchiya: RULE

Hamasaki Ayumi - A BEST and I am..., I borrowed both at the same time.
Dir en grey - Vulgar
Acid Black Cherry - BLACK LIST
MUCC - Kuchiki no Tou
Kitade Nana - I scream
X JAPAN - Vanishing Vision

Mh, I can't really think of more first albums rather of more first songs, 'cos when I got into J-Music people where uploading a few songs most of the time and not a whole album. That's at least how I remember it. :laugh

ayu - A Song for
Koda Kumi - affection
Namie Amuro - 181920
Shota Shimizu - Umbrella
Ai Otsuka - LOVE LETTER
Utada Hikaru - Exodus
GACKT - MARS

Ayu - A COMPLETE ～ALL SINGLES～ / NEXT LEVEL
Kuu - JAPONESQUE
Miliyah - TRUE LOVERS
BENI - Fortune
Namie - BEST FICTION
Utada - ULTRA BLUE

BIGBANG - ALIVE
2NE1 - COLLECTION
BoA - HURRICANE VENUS

Ayu: Rock'n'Roll Circus
BENI: Lovebox
Hikki: Ultra Blue
JASMINE: GOLD
Kana: to LOVE
Kuu: TRICK
Mai K: If I Believe
Mika: STAR
Miliyah: HEAVEN
Namie: BEST FICTION
Rina: ALL SINGLE BEST