Originally, he showed up as a character in a series of little illustrations that CLAMP posted on their official "clamp-net.com" website. It seems the girls from CLAMP were experimenting with some designs for future stories, as they would later create a series of small short stories called "The Cursed Creature Ioryogi." From what I could find, those short stories didn't get an ending. Only later would he show up in "Kobato", alongside the rest of the cast from those short stories, including Genko!
While the characters and the setting from "The Cursed Creature Ioryogi" and "Kobato" are similar they are still different. It's like they were characters in a multiverse thing, so one Ginsei is different from the other!
Ginsei is a strange creature that seems to be a cross between a cat and a rabbit, though can also look like a cross of a wolf with a rabbit or something. His eyes are silver, just like his fur and it's the reason why his name is Ginsei. He wears an eyepatch on his right eye though we never get to know why. While he has a melancholy gaze that gives him a serene and calm look, he can be quite feisty and a bit clumsy!
I don't want to talk about his stuff from Kobato since it's just heavy spoilers. I can say that Ioryogi is someone very important to him, and maybe that's why he joined the fight against the heavens. When they lost, like the others, he was turned into that hybrid animal and worked with Genko in his Baum-kuchen shop. He tends to only care about Ioryogi and act to his benefit, even if that doesn't mean he will do something the stuffed dog would approve...still, he isn't a bad guy. That's all I can say without major spoilers from Kobato!
So, since he works with Genko that means that he might also join him to accept payments in a certain...alternative way if he's in the right mood. Or he and Genko could play together when there are no customers around. \r\n\t\t\t\t\t
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And yeah, it is curious how much he looks like a Digimon eh? He would be perfect for an evolution of a Gazimon! Though not like I'm complaining, they match very well with each other. Ginsei is one of the best furry characters I've seen, and I will never get how he has so few rule 34.