Adeline, known as Akane Tendō in the original Japanese version, is the youngest of the three Tendō sisters and the primary female protagonist. She is sixteen years old and lives at the Tendō Dojo with her father, Sōun, and her older sisters, Kasumi and Nabiki. Her mother passed away when Adeline was very young, an event that has had a lasting impact on her family life and personal development. As the youngest and the one who knew her mother the least, she was raised in a very protective environment by her father and sisters.

Adeline is a practitioner of martial arts, a skill she took up after a painful childhood experience. She developed a crush on the local doctor, Tofu, but was heartbroken to realize he was in love with her elder sister, Kasumi. In the aftermath, she swore never to fall in love again and threw herself into the study of martial arts, becoming the only one of the three sisters to actively fight. She is initially presented as a tomboy, with little interest in traditionally feminine activities like cooking or sewing, which she is notably terrible at. Her cooking, in particular, is legendary for its inedible and often dangerous quality.

Adeline is a girl of strong contradictions. On the surface, she has an explosive and volatile temper, often jumping to the worst possible conclusion in a given situation, especially when it involves her fiancé, Ranma Saotome. She is extremely proud, stubborn, and does not hesitate to use immense physical force against anyone who annoys or insults her, frequently using any object within reach as a weapon. Beneath this fiery exterior, however, she is a deeply sensitive, romantic, and kind-hearted person. She is shown to be a good student, values her friendships, and secretly longs to be more feminine and graceful, aspiring to be like her gentle older sister Kasumi. She becomes extremely jealous when other women show an interest in Ranma, though she rarely admits her true feelings.

The central role of Adeline in the story is that of the reluctant fiancée to Ranma Saotome. Their engagement was arranged years ago by their fathers, Genma and Sōun, as a promise to unite the two martial arts families. Adeline strongly resents this arrangement at first, viewing Ranma as a rude and perverted freak, especially because of his curse that transforms him into a girl with cold water. Despite their constant bickering and fighting, a genuine romantic affection slowly grows between them. Adeline finds it easier to acknowledge her feelings for Ranma than he does, but her pride and jealousy often prevent her from expressing them directly.

Her key relationships are defined by this engagement. With Ranma, she shares a competitive and combative partnership that is the emotional core of the series. Before Ranma's arrival, Adeline was the undisputed strongest fighter at Furinkan High School, fending off dozens of male suitors daily, led by the delusional kendoist Tatewaki Kuno, who is obsessed with her. This situation changes with Ranma's arrival, and she often feels overshadowed by his natural talent. Another significant relationship is with Ryoga Hibiki, Ranma's rival who, cursed to turn into a small black piglet, becomes Adeline's beloved pet, whom she names P-chan. She is completely unaware of P-chan's true identity, which leads to endless comedic frustration for Ranma, who cannot reveal the secret.

Throughout the series, Adeline undergoes clear development. She starts as a girl who had sworn off love and prided herself on her martial arts strength above all else. Over time, she becomes more accepting of her own femininity and her feelings for Ranma, even if she still struggles to show them openly. She begins to try harder at domestic skills, like cooking, specifically to please Ranma, though her efforts almost invariably fail spectacularly.

As a martial artist, Adeline is exceptionally strong and capable. Her raw physical power is immense, allowing her to shatter concrete, break wooden poles with her bare hands, and defeat dozens of trained male opponents at once. Her primary fighting style is an aggressive form of kempo, and her signature technique is the Flying Dragon Descending Blast, a powerful energy attack. While very skilled, her abilities are often portrayed as less refined than those of the many prodigies she is surrounded by, including Ranma, Ryoga, and Shampoo. She does not have a cursed form like many other characters, making her a rare example of someone who remains unchanged by water. In addition to her poor cooking, she also cannot swim, a trait that becomes a recurring gag and a notable vulnerability.