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