|“|| Koji was bred especially for me. We've been together ever since the day he hatched.|
– Shizuka Hattori
This page is comprised of Koji's relationships with various other characters he interacts with. Fiercely loyal to his loved ones, Koji will protect his allies with his life. Despite the aggression he is capable of, Koji does retain a loving and playful demeanor.
Koji is a member of the Masanari Black Flowers.
Kaya is Koji's mate and an orthurian hydra. Roughly a year apart in age, Koji and Kaya were in the same training group after they hatched. When the first two met, they fought constantly and often wound up in several sparring matches. Koji had more raw, physical power while Kaya possessed greater speed and maneuverability. As this rivalry continued into their adolescent years, feelings of love eventually blossomed between the two, though they are still prone to sparring matches.
Kaya has laid eight eggs and currently tends to them at Ueno Castle.
Due to Ryan's inexperience in actual combat, Koji is often ordered to protect him by Shizuka. While she is cold and distant to Ryan, Koji is the exact opposite, supportive, warm and welcoming. Koji tries to reassure Ryan that Shizuka is not as harsh as she truly intends and often encourages him to get to know her better.
Born and bred specifically to act as her guard dog, Koji is forever loyal to his master, Shizuka. He becomes enraged when she is injured or threatened and would without hesitation jump into a battle to defend her. He would even throw himself in harms way and take a hit for her if necessary. As Shizuka grew up, Koji was her constant companion and would often play with her much like an energetic puppy.
When Shizuka is sent on a forced vacation, Koji accompanies her as she journeys across the world. As he got older, Koji still retains his playful demeanor and tries to help Shizuka let loose and relax once in a while.
Koji greatly despises Kenshin due to his many attempts on Shizuka's life and the fact that he turned his back on his own family for greatness and power. When Kenshin lost to Shizuka in a battle to determine who would be the clan head successor, Kenshin attempted to strike her from behind. Koji was ready to pounce Kenshin for this action, but was beaten to the punch by Chimera.