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.
Complete ONE HANDED MILF
Use the JUSTICE LASER special attack
DATE all girls
Find the PERFECT FLATNESS
Finish with the M.I.L.F.
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
Complete ONE HAND NORMAL ROCKY CHAN
Complete NORMAL ROCKY-CHAN
Defeat the Thrasher Super Mecha Warrior
Complete ONE HAND PUCKY K-9 UNIT
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
Complete ONE HANDED SHARP-EYE
Unlock NORMAL ROCKY-CHAN
Unlock PUCKY K-9 UNIT
Get promoted to the F.L.A.T. SPECIAL FORCES
Get a smelling Pantie evidence
Reach 18 STARS
Defeat the Fake Wadding
100% SHARP-EYE YUMIKO
Complete ONE HAND NAO
Get the SHIELD power up
Defeat DP Defender
100% NAO NEKOYAMA
Explode a mine!
Complete ONE HAND JULIA
Unlock METAL ROCKY-CHAN
Unlock SAYRU-CHAN
Get a special Phone Number
Reach 10 STARS
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
Take a photo of a girl
Kick Justice in the balls
Make a 5 STARS stage
100% MIKA MOKOTO
Get the LASER power up
Get the ROCKET LAUNCHER power up
Torn apart your first piece of cloth
Go to your first date
Begin history mode