Here is the full list of all 84 OMORI achievements. It takes around 80-100 hours to unlock all of the achievements on Windows.
Throw away something.
Reach the good ending.
High-five KEL three times.
Defeat HUMPHREY.
Defeat SLIME GIRLS.
Defeat PLUTO (EXPANDED).
Defeat MR. JAWSUM.
Complete all part-time jobs once.
Complete ORANGE JOE's quest.
Turn the valve to the right in RAIN TOWN.
Defeat SWEETHEART.
Kill the first SOUS CHEF.
Perfectly train the SPROUT MOLE choir.
Choose the FALL MOLE.
Choose the SUMMER MOLE.
Choose the SPRING MOLE.
Ruin Christmas.
Choose the WINTER MOLE.
Listen to MR. SCARETHROW's rant.
Go to sleep after a long day.
High-five KEL.
Wake up in the morning.
Make your way and talk to LONE MOLE.
Defeat KITE KID.
RELEASE ENERGY on your foes.
Defeat SPACE EX-BOYFRIEND.
Defeat DOWNLOAD WINDOW.
Gain BREAD using BREAD SLICE.
Defeat THE EARTH.
Fly the BUTT CERTIFICATE in CATTAIL FIELD.
Pet a dog.
Water a plant back to life in BASIL's garden.
Complete your TO-DO LIST.
Reach the bad ending.
Reach the other ending.
Get all rewards from the RECYCLING MACHINE.
Get the LOL SWORD.
Watch all movies in SWEETHEART'S "throne room".
Defeat the CHICKEN? at the top of DINO'S DIG.
Trade CLAMS for CLEMS.
Have a ghost party.
Pet all the creatures in MARINA's sector in HUMPHREY.
Hold 99 TOFU.
Defeat 100 BUNNIES.
Defeat 100 SQUIZZARDS.
Commission ROCOCO.
Commission all of ROCOCO's art.
Commission all of GATOR GUY's statues.
Let the plastic fish finish its song.
Take the KEEPER OF THE CASTLE's power.
Get the FLOWER CROWN from BASIL.
Recover at all of MARI's picnics.
Visit all mirrors.
Look through all telescopes.
Defeat ???.
Defeat UNBREAD TWINS.
Defeat SPACE EX-HUSBAND.
Defeat PLUTO and THE EARTH.
Defeat ROBOHEART.
Defeat MUTANTHEART.
Defeat PERFECTHEART.
Beat the BOSS RUSH.
Defeat every SOMETHING at the bottom of the LOST LIBRARY.
Don't high-five KEL.
Brush your teeth every day.
Take $20.00 from KEL's wardrobe.
Get a perfect score delivering PIZZA.
Quit in the middle of a part-time job.
Go to SEAN and KAREN's housewarming party.
Complete the math worksheet correctly.
Complete the grammar worksheet correctly.
Feed the STRAY CAT every day and sunset.
Lose to KIM and VANCE.
Defeat the HOOLIGANS with PEPPER SPRAY.
Battle the "bees".
Insert every song into GINO'S JUKEBOX.
Defeat the PET ROCK champion.
Defeat the RECYCLEPATH.
Receive all FLOWERS in the hospital.
Read all the tombstones in the... dev room...
Enter code: haveadollariguess at www.omocat-shop.com for $1.00 off.
Unlock all achievements. Thank you for playing OMORI.
Give FLOWERS to MARI.
Complete the FOE FACTS! journal.