Born from a sled dog and a wolf, a artic researcher helping the Kasshus with Earth research had a spare pup that was sick and needed medical attention for it.

Kyoji Kasshu stepped up. Not a doctor nor vet, he offered to treat Nimbus' sickness and nursed him to health. Nimbus' siblings were returned to the zoo, but Nimbus grew hyperattached to Kyoji and stayed. Nimbus would later be gifted to Renee, who he now is hyperattatched to.

From Kyoji's treatments he was actually infected with a 'pure' version of the DG cells before they became the corrupt form show in the anime. It healed him, and intruigingly he has a self recover ability and it can be passed down inhis offspring. He is also immune to being infected by DG cells again.

13th Gundam Fight

He follows Renee across the world and he generally makes friends with everyone he meets. The sister of Neo-Denmark gifted Nimbus his Ladybug Backpack and he will get fussy if he doesn't get to wear it.

During the Gundam Tournament finals, when Ulube sought to use Rain to power the Devil Gundam Nimbus attacked Ulube. He was shot in the attack, but this saved Dr. Mikamura (later arrested by the Neo-Japan government) and led to Nimbus becoming quite the superstar. Despite not being a Gundam Fighter, he's more popular than any of the fighters and is constantly invited to events.

Post Tournament

Nimbus found a mate in a Korean Jindo female and they had a little of pups. One of them, Cwen Annwen, was also albinistic. This pup also had a unique 'antler' mutation and Nimbus is helping research of the healing powers of his DG cells. Renee is debating neutering because Cwen likes to ram his antlers into her when she doesn't feed him on time.