There are 41 treasure chests in the game. You will need to complete the game once and revisit areas on your complete saved file to collect all of them.
Timestamps:
Main Road (1 Chest) 0:31
Castle Town 1st Visit (5 Chests) 0:58
The World Within 1st Visit (8 Chests) 2:45
Forest of Thorns 1st Visit (10 Chests) 8:00
Depths of Darkness 1st Visit (5 Chests) 13:05
Castle Town 2nd Visit (4 chests) 14:56
The World Within 2nd Visit (5 chests) 16:39
Forest of Thorns 2nd Visit (2 Chests) 18:58
Depths of Darkness 2nd Visit (1 chest) 19:56
Here is a video guide with English commentary!
Here is a playlist of guides for this game!
https://www.youtube.com/playlist?list=PL-HeW6XkKdUJAapskRPLA...