Yakitsuki was Pregnant and Aborted
In the world with fetus and umbilical cords, there are a lot of needles, which are used in illegal abortions. In addition, the event with the big doll shows it emptying of blood and more particularly of the belly. The atmosphere of the game is generally calm, with many shades of white meaning that Yakitsuki is depressed and does not assume her act.
Yakitsuki is a Photographer
One effect that Yakitsuki can get is a camera that lets her take photos. There is also a board in her room that fills with photos as she collects effects. Both of these things suggest an interest in photography.
Nature could be Yakitsuki's subject of choice when photographing, as the Camera effect is found in a burnt down forest, as well as a number of the dream areas (Clover World, Dark Mushroom Forest, Wilderness, etc) and effects (Mushroom, Flower Vase) are related to plants/nature.
Yakitsuki's House was Burned
From the Burned Ground we know that it's possible Yakitsuki had a tragedy of losing her house, camera and important people in a breaking out of fire. It might cause by an accident from the microwave which Yakitsuki can find the Microwave effect in the Snow World, considered it connected with Burned Ground.
The Date of The Accident
In the Electronic Tube World, you can find some numbers on the electronic tubes, two of the combining numbers are "2004 06 26" and "12:59:58(9)", possible hinting something happened to Yakitsuki at 12:59 am of June 26, 2004. Since you can find the Snail effect here, it might mean Yakitsuki wanted the rain to extinguish the fire at that time.