The Snow Country Prince

Koichi lives with his sister Yuki in Japan, where they encounter Hanaguro, a swan who migrated from Siberia. After Hanaguro is attacked by a dog, Koichi flees, unable to stand up for himself. However, that night, he has a lucid dream in which he's transported to the fictional Kingdom of Snow Prince, where he discovers the courage to defend other swans. This experience leaves a lasting impact on Koichi.