Here is the full list of all 51 OKAMI HD achievements. It takes around 40-50 hours to unlock all of the achievements on Windows.
Learn how to use Rejuvenation.
Learn how to use Power Slash.
Return Kamiki Village back to normal.
Learn how to use Bloom.
Defeat enemies inside of a Devil Gate.
Learn how to use Cherry Bomb.
Learn how to use Water Lily.
Learn how to use Vine.
Exterminate the Spider Queen.
Defeat the imps that possessed Princess Fuse.
Learn how to use Watersprout.
Learn how to use Crescent.
Learn how to use Galestorm.
Defeat the Crimson Helm.
Enter the Moon Cave.
Learn how to use Inferno.
Make your way to shore without being swallowed by the Water Dragon.
Learn how to use Veil of Mist.
Learn how to use Catwalk.
Defeat Evil Rao.
Learn how to use Thunderstorm.
Win the final race against Tobi.
Defeat True Orochi.
Learn how to use Blizzard.
Defeat the twin demons, Lechku and Nechku.
Board the Ark of Yamato.
Increase your Solar Energy, Ink Pot, and Astral Pouch levels to maximum capacity.
Complete your Fish Tome.
Complete your Travel Guide.
Complete your Treasure Tome.
Defeat all monsters on the Wanted List.
Collect all Stray Beads.
Complete your Animal Tome.
Learn all god techniques to fill up your Technique Scroll.
Complete your Bestiary.
Earn a Cherry Tree rank for each item in the Total Results screen.
Earn a Cherry Tree rank for each item in the Results screen.
Defeat all enemies at all three Devil Gate trial caves.
Defeat the Kusa 5.
Beat Hayabusa's turnip-digging record.
Complete five digging mini games.
Win the race against Ida and Hayate.
Win the race against Kai.
Unlock all achievements.