Someday/theories

In the School World, you can find, in a certain classroom, a child version of Itsuki who is sitting in a chair alone, watching his playing classmates through a window. Itsuki was likely a solitary boy in the elementary because he was different than the other child, most specifically more intelligent than the others. This could explain why you receive the Nerd effect from him, and because of that intelligence the other child regret Itsuki and the only way to be accepted by the others is being like them. This could explain why a classmate of Itsuki sends you to the Monochrome effect location, as an attempt at assimilation. Itsuki would rather be alone than be a part of their groups, but has regrets of his introverted behavior in the Question World.

The NPC from which Itsuki receives the Lab Coat Effect (An adult with colorful wings wearing a lab coat) could be a figure Itsuki looks up to or could potentially be Itsuki himself in the future. Many of the effects and locations relate to science or technology (Wrench, Nerd, Lab Coat, and Clockworker effects, Testing Area, Space World and Hospital), so he is likely interested in science, medicine or engineering. Itsuki may want to become a scientist or researcher when he is older, and that NPC looks very similar to him.

Creation of Itsuki, Kondo
From entry of purple crystal that can be found in place known as Void, revealing that blonde girl from glitch world, Kondo actually is creation of Itsuki, since a little bit artist he drew in his opinion perfect girl, it was Kondo, she been person who he wish to be, but again, in his opinion she been too perfect, so pefect that he hate her, from that Itsuki got inferiority complex, stuck in his own mental shell and had nightmares, but since Itsuki been inventor he created plan how eradicate Kondo, how its been known in Japanese Mythology there is creature that eat dreams, Baku, plan of Itsuki make artifical Baku, in the true end Itsuki who become Baku, absorbed Kondo, cleaned his dreams from her nightmares and even got confidence to let his parents know where he is, cuz in truth, Kondo been not only masterpiece of Itsuki, not only perfect girl, not only person who Itsuki wished to be, hatred of Itsuki turn her in his own, vixen, evil, dark side.