Ginsei is a mysterious creature who appears in Kobato, characterized by his silver fur with subtle gold stripes and silver eyes, the latter being the source of his name, which means silver life. He typically wears an eyepatch over one eye and has a physical form resembling a cross between a cat and a rabbit, standing upright on his hind legs. Despite this small, doll-like appearance, it is implied that his true form is something much larger and humanoid, as his shadow has been seen cast as that of a young man with short hair. Like Ioryogi, his current animal-like state is not his original form but a result of circumstances connected to the heavenly realm.

Ginsei shares a deep and complicated history with the blue canine creature Ioryogi. In the past, Ginsei was found half-dead in the other world by Ioryogi, who took him in, raised him, and gave him his name. This makes their relationship that of a master and student, or a mentor and ward. Ginsei holds significant respect for Ioryogi because of this, but his outward demeanor is often hostile and confrontational. He frequently challenges Ioryogi to fights and speaks to him with a rough, disrespectful tone, demanding to know when Ioryogi will return to Heaven. This apparent contradiction stems from a deep-seated loyalty and possessiveness; his aggression is a misguided way of trying to protect his mentor and ensure his return to his former glory. Ioryogi seems to find Ginsei's zealous behavior somewhat amusing, viewing it as a sign of his former student's unwavering, if clumsy, devotion.

Ginsei's primary motivation is to see Ioryogi return to his true form and station in the heavenly realm. He initially views the young girl Kobato as an obstacle to this goal, believing that eliminating her would free Ioryogi from his obligations in the human world. To this end, he attempts to attack Kobato, but is stopped by Ioryogi, who fiercely protects her. When Ginsei underestimates Ioryogi's power in his small, plush form, he is easily defeated, yet he continues to observe Ioryogi and Kobato from a distance. Despite his stated intention to kill her, his actions reveal a conflicted nature; he is not a true villain but rather a fiercely loyal being who lacks the emotional honesty to properly express his concern for his former master.

As the story progresses, Ginsei undergoes significant development. His role shifts from a would-be antagonist to a more complicated ally and observer. He comes to understand the depth of Ioryogi's commitment to Kobato and the seriousness of her mission to heal a bottle with wounded hearts. While he may grumble and maintain his prickly exterior, he eventually becomes a more permanent fixture in the world of the characters. In the anime's conclusion, after Kobato's wish is granted, Ginsei remains in the human world, joining the others at Genko's Baumkuchen shop. The manga provides an even more profound resolution to his arc. When Kobato is reincarnated and reunites with those she knew, the man she loves, Kiyokazu Fujimoto, has had his memories of her erased. To rectify this and ensure their happiness, Ginsei willingly makes a contract with God. The price for this contract is severe, as Ginsei himself is transformed into a stuffed animal, sacrificing his mobility and his original form to grant happiness to the couple his mentor swore to protect. This final act demonstrates that beneath his abrasive and aggressive exterior lies a deeply selfless and loyal heart, capable of great sacrifice for those he has come to care about, mirroring the loyalty Ioryogi once showed him.

Ginsei is aware of Kobato's mission and the workings of the other world. As a being originally from that realm, he possesses combat abilities that rival Ioryogi's. He is strong and agile enough to push Ioryogi in a fight, even when his opponent is restricted to a small, plush body. His most notable ability, however, may be his tenacity and his capacity to interact with and make contracts with divine powers, as seen in his ultimate sacrifice in the manga.