Haruka Nanase serves as the Vice-President of the Student Council at Babel, the international academy training young people who have returned from other worlds. She is a young woman with long green hair and matching green eyes, and she is almost always seen wearing her standard school uniform, which includes knee-high socks.

As the vice-president, Haruka is characterized by her strict, serious, and highly responsible nature. She takes her duties on the student council very seriously and is committed to maintaining order and discipline within the school, willing to use any measures necessary, including force, to control disturbances. This rigid adherence to rules puts her into frequent and direct conflict with the series' protagonist, Akatsuki, whose irresponsible actions, disregard for school regulations, and perverted habits constantly disrupt the orderly environment she tries to uphold. During one of their initial encounters, Akatsuki deliberately provoked her by stealing her underwear, an act that profoundly embarrassed her and led her to start wearing only lingerie that was difficult to remove, while also cementing her animosity toward him.

Despite her outward disapproval of Akatsuki, Haruka monitors his activities very closely, even going so far as to use a student named Kuzuha as a spy to report on him. Through this persistent observation, she comes to witness his bravery, strength, and genuine kindness toward those in need. She eventually develops a grudging respect for his abilities and character, though she would never condone his behavior. Over the course of the story, she shows signs of developing a deeper affection for him, acting in a tsundere manner and being unable to fully hide her growing attraction. An example of her conflicted feelings occurs when she touches his super-sonic motorcycle, Sleipnir, which triggered a defense mechanism that shredded her clothes; he offered her his jacket, a gesture that made her feel deeply embarrassed and uncomfortable due to his unexpected thoughtfulness. Her respect and feelings are hinted at again when she eventually attempts to set their differences aside to join his group on a trip to the beach, though her hopes for a normal outing are quickly dashed when his perverted side emerges, culminating in an incident where he managed to strip her of her swimsuit.

In terms of abilities, Haruka is a highly skilled magic user, possessing power formidable enough to defeat a Class A student with little effort. She specializes in wind magic, which she has mastered to a high degree. Her signature technique is a unique style of flight magic; she creates a green magic circle under her feet to generate a powerful gust of wind that launches her into the air. She can then fly at incredibly high speeds, using this mobility both for travel and as a combat advantage to overwhelm opponents with quick movements and high-speed attacks. Her signature weapons are a pair of large push knives, which she wields in battle, often combining them with her flight magic to perform devastating diving attacks that use her momentum to add significant force to her swings.