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