Kagerou

When he was still a pup, Shimmer and his mother used to rule the sacred mountain together. One day an adventurer killed his mother but Shimmer himself survived. He ran from the adventurer and was eventually rescued by an elf girl, who was in fact Tiera Lucent. He worked hard in order to get stronger in order to return to the sacred mountain. He was always thankful to her so when they meet again he recognized her scent on Schnee Raizar and agreed to pull their carriage in hopes of meeting Tiera again. After it is discovered by the other that Tiera had saved him when he was younger, Schnee suggested transferring ownership of Shimmer to her instead, with the secondary idea of having Shimmer protect her.