Himika Akaba, also known as Henrietta Akaba in some adaptations, is a central character in the narrative, serving as the chairwoman of the Leo Duel School (LDS) and the mother of Reiji Akaba. She is also the wife of Leo Akaba, the founder of Leo Corporation, and the adoptive mother of Reira Akaba. Her background is deeply tied to her husband's abandonment of the family to search for their daughter Ray in another dimension. This event left her to manage the vast Leo Corporation alone, an experience that hardened her and made her fiercely protective of the institution she controls.

Himika is characterized by a calm and collected exterior that masks a ruthlessly pragmatic and ambitious nature. She is a diligent and level-headed businesswoman who holds the reputation and standards of the Leo Duel School above almost all else. However, behind this professional facade lies a fiercely strict individual who cannot tolerate any loss of face for her organization. She is willing to go to extreme lengths to nourish and protect the LDS, viewing it as an extension of her own power and a necessary tool to combat the coming threat from other dimensions. While she shows concern for her students, this care is secondary to the institution's success, and she can be cold and manipulative toward those she considers obstacles or disposable assets.

Himika’s primary motivation is the protection of the Standard Dimension, but her methods are often authoritarian. Initially, she seeks to absorb other duel schools, such as the You Show Duel School, in order to monopolize new summoning methods like Pendulum Summoning and to gather talented duelists for her own purposes. Her actions are consistently driven by a strategic, long-term plan to counter the invasion from the Fusion Dimension. To this end, she supports the creation of the Lancers, an elite task force designed to fight across dimensions, and uses her media influence to shape public perception, turning potential panic into support for her organization.

In the story, Himika serves as an early antagonist and a figure of authority in the Standard Dimension. She is the one who formally challenges the You Show Duel School, forcing Yuya Sakaki and his friends into a high-stakes duel to prove their worth. As the plot progresses, her role evolves from a corporate rival to a key ally against the greater threat of Duel Academy. She works alongside her son, Reiji, to plan the city-wide defense against the Fusion Dimension invaders. She also orchestrates a worldwide broadcast to reveal the existence of other dimensions and introduce the Lancers as the world's protectors, showcasing her skill in information control.

Her key relationships are complex. With her son Reiji, she has a professional and mutually respectful partnership, even addressing him with the formal Japanese suffix -san. While they share the same goals, Reiji is often disappointed by her more ruthless tactics, particularly concerning her treatment of Reira. Her relationship with her adopted child, Reira, is arguably her most defining moral failing. Himika found Reira in a war-torn area and, after tests, decided to raise her without a "sense of self" to be used as a living weapon against her husband, Leo Akaba. This cold, utilitarian view of Reira as a "duel machine" contrasts sharply with Reiji's more compassionate approach. Conversely, her dynamic with her husband is one of deep hurt and opposition after he abandoned the family, leading her to side with Reiji to stop his plans.

Throughout the series, Himika undergoes notable development. While she begins as a calculating and somewhat villainous figure, her motivations become more sympathetic as the threat from the Fusion Dimension escalates. Her most significant change comes after the final battle against Z-ARC. When Reira is reverted to an infant state due to using the Four Nature Cards, Himika is consumed by guilt for her past treatment of the child. Her obsession shifts entirely from protecting the LDS to restoring Reira's smile, showing a vulnerable and maternal side that was previously hidden. This guilt drives her actions in the final arcs of the story.

As a duelist, Himika is not primarily known for her combat prowess but is capable of dueling when necessary. She notably participates in an Action Duel against Shuzo Hiiragi, the principal of You Show Duel School, though the encounter is more comedic than showcasing her full strategic depth. Her true abilities lie in business management, strategy, and public relations. She is a master manipulator of the media, able to control narratives and sway public opinion with carefully crafted speeches. Her appearance also features a subtle motif; her heart-shaped hairstyle and the English version of her name, Henrietta, allude to the heart suit in a deck of playing cards, reflecting her family's thematic connection to card suits, with her son associated with diamonds.