Five years older than the protagonist and Hikari Hinomoto, Kasumi was their childhood friend and neighbor. She took a commemorative with the protagonist and Hikari at an amusement park before the he moved, eight years before the start of the game. She is best friends with Maeka Kudanshita, as they were classmates in high school.
She is reunited with the protagonist during the second year, when she is appointed as an education apprentice at Hibikino High School. After graduating, she became the protagonist's homeroom teacher. She teaches Japanese.
Although she is a caring teacher in front of her students, sometimes she reveals her true feelings to the protagonist. Like Shiori Fujisaki, who served as the main heroine in the previous game, Kasumi's ending can be quite difficult to get as she only appears during the second year of the game and the player has a limited amount of time to raise her affection.
She is in good terms with Hikari, and they often talk about past events like good childhood friends.
Her presence in the novel version becomes a impact on the relationship of Hikari and Takeru Iwase.
- In a certain event, she acts unexpectedly childish when she sees a stuffed toy in a fancy shop, revealing a side she rarely shows in front of others.
- Her hobby is playing the piano.
- She likes driving and taking baths. She dislikes waking up early and tinkering with machines.
- Her image color is green, and her image flower is kasumi grass.
- During battles, her special skill involves scolding the "persuasion of sincerity" of the enemy.
- Kasumi's character theme is titled "Sugao no Omomuku Mama ni". She has many character songs, but the one based on the melody of her theme is titled "Arashi ga Hajimaru Toki".
- She was voted as the third most popular character. However, it has opened a big water with the upper two characters.
- Kasumi can be disguised as Princess Melora from the TwinBee series, wearing her dress and her tiara.