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