Here is the full list of all 69 Deep Space Waifu: FLAT JUSTICE achievements. It takes around 2-3 hours to unlock all of the achievements on Windows.
Get the F.L.A.T. Multipass badge
Reach 10 STARS
Take a photo of a girl
Defeat Dickus second form
100% PUCKY K-9 UNIT
Get the MACHINE GUN power up
Get the SHIELD power up
Kick Justice in the balls
100% MIKA MOKOTO
Make a 5 STARS stage
Get the LASER power up
Use the JUSTICE LASER special attack
Get the ROCKET LAUNCHER power up
Torn apart your first piece of cloth
Go to your first date
Begin history mode
DATE all girls
Unlock SAYRU-CHAN
Unlock SHARP-EYE YUMIKO
Unlock METAL ROCKY-CHAN
Unlock NORMAL ROCKY-CHAN
Unlock PUCKY K-9 UNIT
Unlock SERGEANT CHIKARA
Unlock M.I.L.F.
Find the PERFECT FLATNESS
Unlock the SECRET SPY
Defeat DP Defender
Defeat Dickus first form
Defeat DP Miner
Defeat the Fake Wadding
Defeat DP Mothership
Defeat the Thrasher Super Mecha Warrior
Defeat Dickus third form
Destroy the Sneak Mothership
Defeat Dickus final form
Finish with the M.I.L.F.
Get the RAY power up
Get a special Phone Number
Get a smelling Pantie evidence
Get the super scret spy business card
Reach 18 STARS
Reach 30 STARS
100% JULIA SUZUHARA
Complete ONE HAND JULIA
100% NAO NEKOYAMA
Complete ONE HAND NAO
Complete ONE HAND MIKA
Complete SAYRU-CHAN
Complete an ONE HANDED SALE
100% SHARP-EYE YUMIKO
Complete ONE HANDED SHARP-EYE
100% METAL ROCKY CHAN
Complete ONE HAND METAL ROCKY CHAN
Complete NORMAL ROCKY-CHAN
Complete ONE HAND NORMAL ROCKY CHAN
Complete ONE HAND PUCKY K-9 UNIT
100% SERGEANT CHIKARA
Complete ONE HAND SERGEANT CHIKARA
Unlock LIME CODE
100% LIME CODE
Complete ONE HAND LIME CODE
100% M.I.L.F.
Complete ONE HANDED MILF
Get promoted to the F.L.A.T. SPECIAL FORCES
Infiltrate in the secret TENTACLE organization
Be spotted by the enemy
Explode a mine!
complete 100% the spy
complete ONE HANDED SPY