"Hello Halley" is an original song that was sung by Luo Tianyi in 2013. In 2016, a remastering featuring Stardust was uploaded and gained more popularity than the Tianyi version.
In the song, Stardust is a 'space mailman' delivering a letter to someone/something named Halley. She expresses regret that she cannot bring them/it along with her, and becomes nostalgic about the past. Before leaving, she asks Halley to remember her the next time they meet again.