A mysterious girl who doesn't reveal much about herself. A first year student of Eiden school but wise beyond her years. Natsume can be found in strange places but she acts as though it were purposeful. Natsume prefers to refer to people by their last name. She is not good at remembering names, but will instead create nicknames for them. She calls Sakura "Umeko" and Rin "Suzu".
Natsume hints to have knowledge of the secrets of the island and the secret behind the Principal. Natsume is openly hostile towards the Principal and refers to her by her first name out of disrespect. She also reveals that she is searching for her father and she last heard that he was on Eiden island.
Kazushi first met Natsume at the boys' dormitory where he fell asleep lying on the grass looking at the stars. Natsume prodded Kazushi but he did not respond thus she assumed that he was dead. She decided to toss him into the sea. Kazushi woke up and rose up quickly, and his face collided with hers. Kazushi and Natsume shared their first kiss accompanied by cut lip on both parties. Natsume flew into a rage and attacked Kazushi, and he managed to calm her down and offered her his friendship.
A few nights later, Kazushi found Natsume wandering around the boys' dormitory again. Kazushi suspects that she was looking for something and asked her. She claims that she was looking for herself. Left in confusion, Kazushi offered to help her search anyway.
The next day, Kazushi was running low on money. If the player chooses to decline Haruka and Mei's offer, Kazushi will find Natsume having bread for her lunch. He explains that he is hungry and she shares her bread with him.
A few days later, the Principal punished the group when Rei attempted to frame Kazushi for stealing the exam question papers. She commanded them to watch over her alchemy experiment overnight. The experiment caused strange effects on the girls and Kazushi started to panic. Rin disrupted the experiment. Natsume then showed up trapped in a large beaker.
Natsume confronted the Principal and hinted that she knew what the Principal was attempting to do. Natsume was then introduced to Kazushi's friends. The group found Natsume to be adorable and they fawn over her. Natsume was uncomfortable with the attention and hid behind Kazushi.
On Natsume's path, Sakura dressed Natsume up in a cat costume. Natsume ran away from her and Sakura requested Kazushi to look for her. Natsume requested Kazushi to look for her father. After some deductive reasoning, Kazushi concluded that Miya was Natsume's father. Miya revealed that he was involved in a large-scale alchemy experiment with the Principal to create a Noblemen's Stone. Natsume showed up to stop the experiment by eating the incomplete stone and she fell into a comatose state for several years.
Kazushi and Miya found Natsume's body in an underground cave. Kazushi entered her dream to wake her up. Natsume explained that she manifested physical images of herself around the island. Later, Natsume and Miya explained how alchemy works. There exists an ideal world where a copy of everything in the real world exists in a perfect state. Alchemy is the process of trading an item from the real world with that from the ideal world. When Natsume swallowed the stone a few years ago, her spirit was trapped in the ideal world. Kazushi was revealed to have a special ability to freely travel between both worlds.
Miya found his protective fatherly love for Natsume and he decided to work at the school's shop to be closer to Natsume. He brought his katana with him as a symbol of his protective love.
Some time later, the Principal decided to act and retrieve the Noblemen's Stone from within Natsume. She conducted a large-scale experiment to sacrifice everyone in the school to complete the stone. Everyone's spirit was sent to the ideal world and Natsume uses a katana to "kill" them in the ideal world to wake them up and return them back to the real world.
Unfortunately, Natsume and Kazushi was trapped in the ideal world when the Principal's experiment was ended by Miya. The Principal then realized the error of her ways and remembered the value of human relationship.
The Principal suggests that Natsume and Kazushi destroy the copy of the island's Noblemen's Stone in the ideal world to escape it. She knows that that act will cause the destruction of the Stone in the real world as well. She will not be able to satisfy her own desire but she explains that she has moved on.
Edelweiss Eiden Fantasia
On Sakura's path, Natsume was revealed to have poor social skills. Kazushi and Sakura found her attempting to manage Miya's store while he was away and they volunteered to help.
On Rin's path, Natsume appeared to investigate Poko. She later rescued Kazushi from the Principal's hands.