List of Missable Achievements

There are a total of 15 achievements that can be make permanently inaccessible on a player's save file.

All 7 of the "take no damage" achievements can be missed by simply progressing the plot.

(01) (02) (03) (04) (05) (06) (07)
23 Red Jewels become permanently missable by the plot progression, locking the player out of the following 3 achievements.

(08) (09) (10)
And finally, there are 5 misc. achievements that, as with the others, can be missed by progressing the plot, but are also missable by just not being aware.

(11) (12) (13) (14) (15)

Spoilers!

Only expand the following if you don't care about spoiling the game.

Points of No Return (and Missable Items)

There are a lot of places in the game where parts of the map become inaccessible. This is a list those turning points.

Note: In addition to the mentioned locations, all previous locations also remain locked.

Leaving Edward's Castle with Kara prevents further access to Edward's Castle (2 Red Jewels) and Edward's Castle Dungeon (2 Red Jewels).
Leaving Itory Village for the Moon Tribe Camp will prevent further access to South Cape. (3 Red Jewels)
Beating Castoth at the Incan Ruins will prevent further access to the Inca Ruins (1 Red Jewel) or Itory Village (1 Red Jewel).
Initiating the Riverson cutscene on the Gold Incan Ship (by examining the dead queen) will prevent further access to the ship and Seth. (1 Red Jewel.)
Leaving Oakton (the Diamond Coast cottage) and going to Freesia after will prevent further access to the Oakton. (1 Red Jewel. This is also where Turbo is.)
In Freejia, talking to Erik after using the Memory Melody will move the player to Neil's Cottage, preventing further access to Freejia (3 Red Jewels, 1 Health Upgrade) and the Diamond Mine (3 Red Jewels).
After beating Viper in the Sky Garden, the player moves to the Seaside Palace, preventing further access to Nazca and the Sky Garden (2 Red Jewels).
Beating Jackmond and Silvana (the vampires) in Mu will prevent further access to Mu (1 Red Jewel) and the Seaside Palace (3 Red Jewels).
All locations between Angel Village and Dao remain open up until the final save point (and spirit teleport to Dao) in the Towel of Babel.