Similar concept as the swan picture a few deviations ago, though this was actually started before that one and was dropped because I couldn't manage the wings at that time. Picked it up again since I figured it out. No references except for the bird.

Lark and Shiru.

The lark is a type of songbird. To mark its territory, it will randomly fly right up into the sky, sing, and descend again. It is associated with ascension in general, which was the last you saw of Lark before he went playing decoy, while his sister Shiru tended to be seen descending from the sky and her name means "song" or something like that in Hebrew. Lark died, she completed what Lark couldn't full bring.
In a way, they also embody sacrifice and forgiveness, two sides of the same coin.