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