In a world in which each person has a Holy Grail that can summon a Servant, Koharu summoned Galahad Alter. She is a new generation of magus and the star of the Holy Grail War Tournaments. She represents the Riedenflaus family who are funding Akihabara's Holy Grail tournaments. Koharu’s family, the Riedenflauses, are renown for making homunculi. Nzambi confirmed that Koharu is a homunculus. Koharu was initially meant to be disposed of because of her current state. As she is a Homunculi, the initial plan was to recycle Koharu and turn her into pure medium and reused for the other homunculi, essentially recreating another using whatever they can.
Koharu wears the uniform of the Mage's Association. She is a short and pale child, perhaps old enough to be in the upper end of elementary school. When Koharu merges with Galahad she grows older. Taller and with a slightly deeper voice, she appears to be in her late teens, about a ten-year age difference.
Koharu is a bashful girl who is easily embarassed, but she does have pride in her abilities. She seems quick to anger. Despite all the feats achieved by humans with verifiable evidence to back it up with the existence of Servants and other means, she believes it to be highly unlikely that humanity even had the technology in 1969 to reach space, let alone send someone to the moon.
She reverses her name "Koharu" to "Haruko" as an alias in public.
The Boy Among the Stars
Nostalgic City Shinjuku
As Koharu is now cursed by Nzambi after their battle, the Riedenflaus family couldn't reuse whatever is left of Koharu and entirely abandoned her, while creating several replacements to take her place. It is then we learned that the summoning of Galahad is actually deliberate as people of Mosaic City cannot actually choose which Servant they will be getting and is decided entirely based on desire and compatibility. Riedenflaus family, however, owns the catalyst (Galahad's sword belt) to manipulate the Holy Grail into summoning the exact servant they desired, effectively cheating the system. Such actions are actually illegal and outlawed but the process isn't new as there are several humans who did the same thing to get the Servant they want (there is even a black market for it). Koharu was also the first Homunculi in her family to successfully manipulate the summon target utilizing the catalyst to get the results they wanted.
The wounds that Nzambi inflicted on her has damaged her Magic Circuits to the point that utilizing Command Seals and her Possession mode became no longer viable. Other than that, she was mostly fine and will eventually make full recovery. Though cursed, she's still lucky as the damage Nzambi inflicted on her wasn't terminal to the point of converting her into a zombie, thanks to the prevention by Galahad while in Possession mode. It is important to note, forcing herself to enter Possession mode or utilizing her Command Seal any further will endanger her Magic Circuits and make them entirely unusable. When Karin offered Koharu an attempt to cure Koharu of the curse, Koharu rebuffed her offer as doing so hurts her pride as a member of the Riedenflaus family.