Moka Akashiya is the central female character of Rosario + Vampire, a vampire attending Yokai Academy, a school for monsters. She is the first person Tsukune Aono meets when he arrives at the school, and she becomes his primary companion and love interest. Her most defining trait is the dual personality created by a rosario, a cross-shaped necklace she always wears. This rosario seals her true vampire nature and creates a gentle, kind-hearted outer personality known as Outer Moka. This version has long pink hair and green eyes, is academically gifted, ranking in the top teens on school exams, and possesses a cheerful, naive, and trusting demeanor. Prior to the series, she was distrusted and shunned by humans in the human world, which made her initially wary of them, but meeting Tsukune helps her overcome that distrust.

When the rosario is removed, the seal releases and her inner personality, Inner Moka, emerges. Inner Moka is her true self, an aristocratic, aggressive, and arrogant vampire with silver hair and red eyes with slit pupils. She is a formidable fighter who relies on powerful kicks and possesses superhuman strength, speed, reflexes, and regenerative abilities. She is cold and dismissive toward most others, often ending confrontations with the catchphrase Know your place. Despite this, she gradually develops a softer, more protective side toward Tsukune, initially claiming interest in him only for his blood but eventually showing genuine care and even romantic feelings.

The rosario does not seal Moka's power but rather her memories and the First Ancestor blood she inherited from her mother, Akasha Bloodriver. As a newborn, Moka was injected with this blood to save her life, but it also linked her to the ancient vampire lord Alucard. When Akasha was attacked, Moka's First Ancestor blood awakened, which in turn awakened Alucard. To protect her daughter and seal Alucard again, Akasha created the rosario and the Outer Moka personality, a clone of herself with wiped memories, to act as a guardian while the true Moka slept. Only someone who truly cares for Moka, specifically Tsukune, can safely remove the rosario, though extreme emotional trauma can also break the seal.

Moka's role in the story is that of the protagonist's anchor and the key to the series' central conflict. Her relationships are deeply intertwined with this dual nature. Her bond with Tsukune is the most significant; he is the only person who can safely remove her rosario, and his blood sustains her. She also maintains close friendships with her classmates Kurumu Kurono, Mizore Shirayuki, and Yukari Sendo, who become part of her found family. Her family background is complex and often antagonistic, involving her father Issa Shuzen, her mother Akasha Bloodriver, her stepmother Gyokuro, and her half-sisters Kokoa, Kahlua, and Akua Shuzen, who frequently oppose her.

Throughout the series, Moka undergoes notable development. Outer Moka becomes more assertive and protective, while Inner Moka slowly opens up, learning to trust and even show vulnerability. Their relationship evolves from being two completely separate entities to a more integrated coexistence, with both personalities eventually acknowledged as real parts of Moka. Her abilities as a vampire are formidable, including immense physical power, rapid healing, and heightened senses, all of which are fully unleashed only when the rosario is removed. She also has an aversion to water, which has a harmful effect on vampires. Overall, Moka is defined by her duality, her protective nature, and her journey from isolation to trust and love.