As of v0.10, Someday implemented Crystals as a new type of collectible. Outside unlocking Menu Theme 8 by finding all of them and them giving hints about Itsuki's past, they are not required to complete the game.
There are 7 crystals, each of a different color, scattered across the game, this page lists them as well as their location.
Crystals
Red Crystal
Location: Found at the end of the Thread World.
Orange Crystal
Location: Found at the end of the Four Seasons Path.
Yellow Crystal
Location: Found at the end of the Space Party.
Green Crystal
Location: Found at the end of the Overgrown Caves.
Teal Crystal
Location: Found at the end of the Playground.
Blue Crystal
Location: Found at the end of the Dance Flood.
Violet Crystal
Location: Found at the end of the Memory Graveyard.
Trivia
- In v0.10, finding each crystal showed a short diary entry written by Itsuki relating to one of his past experiences and could be re-read in a folder of the Computer World, in v0.10+ these diary entries were replaced by picture cutscenes.
- Based of the diary entries, the chronological order of each crystal was: Teal -> Orange -> Green -> Blue -> Yellow -> Red -> Violet, with the violet crystal's entry taking place just a few days before the events of the game.