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.

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.