Haruka Mizusawa is a young man with an apparent age of 22 who serves as one of the main protagonists. His origin is unique, as he is neither a human who received Amazon cells nor a pure Amazon experiment. Instead, he is a third-type Amazon, created when Nozama Pharmaceuticals executive Reika Mizusawa implanted her own human genes into Amazon cells. This makes Reika his genetic donor and, in a very real sense, his mother. He was effectively born two years before the story begins and has no memories of any time prior to that, having been raised in isolation by his adoptive mother, Reika, who kept him sheltered from the outside world.

At the start of the narrative, Haruka lives a quiet, confined life in Reika's home, believing himself to be a human with a weak constitution who requires daily medicine to survive. His personality is initially meek, shy, and kind. He is a gentle person who dislikes fighting and does not wish to harm anyone, a trait that is reflected in his hobby of raising tropical fish in a large aquarium. However, this peaceful existence is a carefully constructed illusion. The medicine he takes is actually a control agent designed to suppress his Amazonian instincts. The day he stops taking his injection, his true nature awakens, guided by an instinct that draws him to a battle between a pest control extermination squad and an Amazon.

This awakening plunges Haruka into a severe identity crisis. He is horrified to discover he is a monster, yet he is also confronted by a deep, violent bloodlust that emerges when he transforms. His core motivation becomes a desperate need to understand his own existence and to prove his humanity to himself. Unlike Jin Takayama, the rider known as Amazon Alpha, who is driven by a singular, ruthless goal to exterminate all Amazons, Haruka clings to a more compassionate and conflicted philosophy. He famously declares that he will protect whoever deserves to be protected and hunt whoever must be hunted, regardless of whether they are human or Amazon. This ideal puts him in direct opposition to Jin's absolute stance, as Haruka cannot accept the indiscriminate slaughter of Amazons who have not harmed anyone and only wish to live peacefully.

His role in the story is that of a protagonist caught between two worlds. For a time, he works with the Nozama Peston Service extermination squad, using his powers to hunt rogue Amazons that prey on humans. However, his empathy for his own kind constantly creates friction with the squad's more pragmatic members. He is tormented when he hesitates to kill an Amazon who shows human-like fear and pain, and he is deeply shaken after secretly releasing a group of unawakened Amazons, an act of mercy that ultimately leads to tragedy. Over time, his role evolves from a confused weapon into a determined protector. He ultimately chooses to leave the extermination team to lead a community of surviving, peaceful Amazons into hiding, becoming their guardian against hunters like Jin.

Haruka's key relationships define his journey. His relationship with his sister, Mizuki Mizusawa, is central; she represents the human family he wishes to belong to, and his desire to protect her is a powerful driving force. His relationship with Jin Takayama is the most complex, evolving from that of a mentor and student to a bitter, reluctant rivalry. While Jin shows him the truth and gives him the tools to fight, their opposing ideals make them enemies, though a strange, grudging respect remains between them. He also shares a deep bond with Mamoru, a fellow Amazon, as they both seek a peaceful existence away from the conflict.

Haruka undergoes significant development throughout the series. He begins as a naive, sheltered boy, unsure of his own identity and horrified by his violent nature. Through painful experience, he matures into a resolute and weary warrior. He learns to control his instincts and masters his fighting abilities, but his idealism is constantly tested by the brutal reality of a world where coexistence seems impossible. His early hesitation in battle gives way to decisive action, yet he never fully abandons his core desire to find another way, a struggle that isolates him from both humans and Amazons at different times. His journey is one of self-acceptance, learning to embrace his monstrous power not for destruction, but for the protection of those he deems innocent.

As Kamen Rider Amazon Omega, Haruka possesses formidable abilities. He can transform using the Amazons Driver, which grants him a sleeker, more controlled form than his initial, bestial Amazon Origin state. In this form, he has superhuman strength, speed, and durability. His body is covered in Wilder Skin that can harden to resist damage and a Converter Lung that can absorb heat and wind to replenish his energy. His primary weapons are the Shellcut Gloves and Boots, which are powerful blades capable of cutting through almost any material, allowing him to perform his signature finisher, the Violent Punish, which bisects his opponent. He can also project sharp spikes from his body when under extreme emotional stress. Furthermore, he possesses a powerful regenerative healing factor, allowing him to recover from severe wounds, which is further enhanced by consuming protein. He can also summon a personal motorcycle, the Junglaider, which syncs with his Amazon cells. Later, he gains access to the Neo Amazons Driver, which allows him to become Kamen Rider Amazon New Omega, an armored but incomplete-looking form that further increases his power.