Even before he breached out of hyperspace before Akiha and Imoko, it quickly becomes apparent that Leopard has an intricate and extensive prologue with the Shishido family. Considering his construction was financed by the Shishido Conglomerate and his fundamental programming seeing its roots in Friedrich Otto Noblemain after Nerval performed as expected, it could be argued that the aristocratic and eccentric Leopard is in a sort of family feud with his siblings who consider him the black sheep of the family. Even though he usually spends time alone in his room exciting himself into laughter and enjoying brewed tea before also taking to playing around on Akiha's laptop, Leopard realizes the high stakes involved as he charges Akiha the retrieval of specific components that were unjustly arrogated. It is for this reason that Leopard repels Benkei's persistent attempts to steal his mirrors so fiercely—even to the point of once conducting a surprise counterstrike on Benkei.
Leopard and Akiha's mutual interdependence exponentially develops over the course of the series because it is only by Akiha's assistance that the Leopard Cannon is successfully discharged while at the same time Akiha is guided through truly appreciating life for the gift it is. There is an arc near the end where Leopard annoys Kazane with his insistence on immediately rescuing Akiha heedless of its futility that suggests he has come to care about Akiha very much. Leopard has two creatures he has personally named residing in his colony, one of which is a crocodile-like creature named Crocodilias Leopardus, which is shown to have three younger Crocodilias. The other creature is an octopus-like creature named Leoparda Octopada. There is also a headless ghost which wears a golden armor and stays in the library.
Leopard has a dark side, who introduces himself as the "Prince of Darkness". The only difference is the eye colour which is blue. According to his dark side, 50 years ago, Leopard was the one who dominated the world with tremendous power and blanketed it with fear. When Benkei came to challenge him to a duel, Leopard has already switched to the dark side of his and even used his sword to damaged Benkei badly. He did not even allow anyone to enter his room. According to Fon, it is the swords that is cursed and awakened Leopard's dark side. His dark side does not require Akiha to activate his "Soul Shout" energy attack as he defeated Nerval by himself. He also recruited Nami.