Kasumi is just like any teenage girl: she wants to enjoy her life. She loves her family very much and, when her father went missing, she wanted to restore his honor so her family would be together again. She had a relatively sheltered upbringing so she doesn't always know how to react to society's standards.
While she does have her rivalry with the Kyokugen practitioners with Ryo being for responsible for her father's disappearance, her wish to find her father seems to take higher priority in the KOF series.
Cutting Projectile - She can fire a projectile of cutting energy from her hands.
Sense - She can sense the presence of people nearby.
English Proficiency - As of Art of Fighting 3, it is heavily implied that she can speak some conversational English. This skill is downplayed in The King of Fighters series.
User of Todohryu Aikijutsu, a form which employs Kendo, Kobudo and Aikido. Her moves relies on counter grabs, using her father's Kasaneate (Piling Hitter) and her high priority kicks. By the time of The King of Fighters 2000, she gained multi-input moves that allows her to chain different attacks.
Masae Yumi - Art of Fighting 3~The King of Fighters XI
Kasumi is said to be learning English as a second language. This can be seen throughout various games that Kasumi appears in.
In many games that she appears in, she tries to taunt her fallen opponents after the battle with an English one-liner in her Japanese to English dictionary phrasebook. She settles on "Come back when you grow up!"
In her first encounter with Ryo in Art of Fighting 3, she believes that he doesn't speak Japanese, she pulled out her dictionary and tried to speak English, but much for her relief, Ryo tells her he can speak Japanese perfectly while proceeding to challenge him.
In KOF 2002 UM, during her MAX2 desperation move, the shadow of her father will appear suddenly and both will release a more powerful version of her Cho Kasaneate, afterwards, he'll disappear, leaving Kasumi confused.
In the Neo Geo Freak's 1997 Volume 8 character poll, she was voted as the twenty-second favourite character with a total of 459 votes. And in the character popularity poll on Neo Geo Freak's website, she was voted as the twelfth favorite character with a total of 973 votes.