Ultra Violet/theories

Sometsuki is/was Being Bullied
All of the chasers in the game look very much like schoolgirls, possibly representations of people who picked on Sometsuki at some stage.

One area in the game is a school-like library, where all but one of the NPC's (a non-hostile chaser) has an unviewable face. This could imply that Sometsuki wasn't close to people in her school/had very few people to rely on.

Bullying Because of Envy
Many of the effects (Rabbit, Coat and Muffler, Cake, Shikkenken, Sea Hare, Android, Ribbons) makes most NPCs to follow Sometsuki. The possible reason is that in reality it can be pretty things, because of which a lot of people paid attention to Sometsuki, that didn`t like the chasers.

Red Water World
The Red Water World (the area where you get the Short Hair effect) is one of the darkest areas in the game. The scissor statue where you get the effect is blood-stained.

The chasers in this area represent people who bullied Sometsuki and at some stage forcibly cut her hair short.

Sleepwalking
One possible reason that Sometsuki won't leave her room is because she's a sleepwalker, as noted by her title in the menu. She may have had a history of waking up in weird places after sleepwalking, after which she started locking herself in her room to prevent that.

Sometsuki Was Betrayed
In the past Sometsuki had a girlfriend,(aka,The girl from the Green house from the Green plant world,and also gives you the Green menu theme.) So,let's call her Midoriko. Sometsuki and Midori were close, really close. It can be proved by the fact that Sometsuki can easily lie down on the bed while Midoriko was sleeping on it. But one day, everything changed, when Sometsuki just took a peak on Midoriko's Diary, it made Midoriko very angry. And after that, They start to quarrel and break up. But not all has been easy as it seems, judging by the creepy appearance of Midoriko in the Uboa event. it seems that she was the one who began to bully Sometsuki and had an idea that she will create a band. A band of bullies whom listens to her orders/demands and starts to bully Sometsuki instead of Midoriko,in fact,Sometsuki was betrayed.