Hakuya no Nightingale

Ravelin and Jenkin are two brothers who, in their childhood, have only had one friend, the arrogant Stefanne. The two brothers have always been warned not to go near the White Flame Lake, the only lake that does not freeze during winter and where you can hear the song of a very rare bird. One day, Ravelin enters the forest that surrounds the lake, determined to discover the origin of the song of the bird, but a terrible tragedy looms around him and the lives of the two brothers will never be the same again.

(Source: Arechi Manga, translated)