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