Official art of Sonoko. (Source)
Garden child (苑 = Garden, 子 = Child)
Sonoko is the protagonist of -1 -Minus Ichi- (-1 -マイナスイチ-). In the game, she is traveling on an empty bus. She refuses to leave her seat so the only things you can do are enter her dream world or write in a diary.
Sonoko has near shoulder-length gray hair and brown eyes. She typically wears a plain white shirt and a yellow skirt. Sonoko also wears a blue jacket over her shirt and brown boots.
Sonoko can also wear different outfits depending on what effect she has equipped.
Much of Sonoko's personality is left to the player's interpretation. Given the light nature of Sonoko's dreams, as well as the relative lack of dark/suspenseful areas, it can be inferred that Sonoko is one of the more lighthearted fangame protagonists.
Very little is known about Sonoko's past aside that she is now traveling on a bus to an unknown destination.
One event in the dream world involves her crying at the bedside of a blonde-haired girl, probably a friend/relative of hers who is sick and/or dying.
The room where you find the weapon effect contains an old projector showing Sonoko with another girl, potentially a childhood friend.