Sola's story revolves around Yorito Morimiya, the main protagonist, who is a young boy attending high school. He loves taking pictures of the sky at any time of day and any time of the year. One day, Yorito decides to take a picture of the sunrise overlooking the bay, but is deterred when he meets a strange girl trying to force a vending machine that stole her money to give her what she tried to buy — a can of tomato juice. Yorito helps her with forcing the machine while attempting to strike up conversation with her, despite it being four in the morning. Yorito tells her why he is here, but by the time he has forced the can out of the machine, the girl has mysteriously vanished.
The next day, Yorito goes to visit his older sister Aono in the hospital with his friend Mana and Mana's little sister Koyori. Despite it being Aono's birthday, Yorito leaves soon after to take a photograph of the setting sun near an old church on the roof of the hospital. That night, Yorito leaves to buy groceries when it begins to rain and stops on the way home to wait for the rain to stop; while waiting, he runs into the strange girl he met from yesterday again. They talk longer this time and Yorito finally learns her name — Matsuri Shihō. A few days later, Yorito goes looking for the girl in the old church and finds a man wielding a sword before Matsuri.
After a display of Matsuri's astounding powers, Yorito discovers that she is in fact a creature known as a "Calamity of the Night" (夜の災い, Yoru no Wazawai?), who has lived for centuries. She is being chased by Takeshi who intends to kill her, but Yorito tries to protect her by bringing her back to his home which is when Yorito asks her to stay with him for the time being.
A "Calamity of the Night", otherwise known as a Yaka is a supernatural being in the Sola story. Yaka have many supernatural powers, such as: a strong physical ability, fast regeneration, and never aging body, among other powers. A Yaka is hurt by direct exposure to sunlight, but the wound can be healed in time if the exposure is not excessive; a Yaka is otherwise immortal unless exposed to too much sunlight or has received fatal wounds. Matsuri explains that a Yaka is the embodiment of human agony and pain and that such creatures are meant to always be alone.