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