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.
Associated Journal Entry: Entry #47: August 24, 2008
I just had the most disgusting feeling today. Mom isn't like this. She's not a bad person. But neither is Dad. He's just busy... really busy... all the time. She won't stop crying from time to time. She says she's not needed. But I do need her. But Dad is not a bad person either...
Orange Crystal
Location: Found at the end of the Four Seasons Path.
Associated Journal Entry: Entry #7: May 10, 2006
I think I'm better off alone. Why even bother? If I'm THAT different, I might as well not try to make friends at all. I'm used to being alone. I can live with that. I don't even like birthday parties anyway.
Yellow Crystal
Location: Found at the end of the Space Party.
Associated Journal Entry: Entry #43: June 11, 2008
You know how a lot people feel that we're all connected in some way? I always felt like I'm missing a link. And now I know why. But it's too late. Still, some part of me knows it wasn't intentional. I believe they really did love me. They really tried to make things better. I just wish I had the chance to tell them I survived. To tell them I loved them. Even if I don't remember them. Wherever they are...
Green Crystal
Location: Found at the end of the Overgrown Caves.
Associated Journal Entry: Entry #25: March 31, 2007
I saw a fox today. They say foxes are really shy, but this one kept staring at me. I think it enjoyed my company! It was really cute. Animals always take it easy, you know? They don't seem to care about the stupid things us humans dedicate so much time to. I wish I took it home. I've named it Miru.
Teal Crystal
Location: Found at the end of the Playground.
Associated Journal Entry: Entry #3: February 7, 2006
Growing up is really weird. I keep asking myself about these wooden dolls I used to play with. But Mom says she doesn't know what toys am I talking about. I'm pretty sure I remember playing with wooden cubes with shapes and colorful letters on them. When I was... Three? Four? I'm not sure.
Blue Crystal
Location: Found at the end of the Dance Flood.
Associated Journal Entry: Entry #36: November 3, 2007
I think I just found out why Mom doesn't like the sea. She had an accident. She doesn't want to talk about it... but she has a big scar on her head. I saw it last night, hidden inside her hair. Maybe that's also why she moved to this city? Her parents' old house is next to a cliff. But we never got to visit it.
Violet Crystal
Location: Found at the end of the Memory Graveyard.
Associated Journal Entry: Entry #49: September 19, 2008
i had an idea. i just drew this perfect girl. her name is Kondo. she is pretty and smart and she is not adopted and everybody loves her because she is perfect. but i hate her because she is who i want to be i feel terrible haha. if i was Kondo everything would be over.
Note: punctuation was added for this particular journal entry for clarity, the original didn't have punctuation from the third sentence onwards and senteces were separated only by line differences.
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. Finally, v0.11 allowed the player to choose between seeing the crystals as animated cutscenes, plain text, or a mix of both.
- 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.