This beautiful and strange relic of times long past or so they claim is the prized procession of the reborn God of the Moon and eldest son of House Aion. It goes by many names since some claim the age of the Seelie Kingdom before the Lunar Calamity. Other Teyvet historians argue it is much more recent. Some even claim it was there when Lord Vesperus was born. However very few remain now that know the truth of his beloved Liyue style flute. Those that do know and remain are either part of the neighboring continent of Arcadia, the land of elemental races or are close retainers to the Celestia royal family.
The truth is Vesperus's flute was a gift from his late godfather, Zhongli the former first generation geo archon and the adepti. The flute once belonging to the Goddess of Dust herself. The flute once one of her beloved keepsakes. It was later learned during one Lantern Rite that the flute had been a part of the gifts for the marriage contract between Zhongli and Guizhong. The flute itself is made from a mysterious crystal-like ore lined with gold, a gold tassel on the end of it.
If a human or mortal tried to play it at best it would just sound broken and unplayable. However in the hands of Vesperus or another deity or elemental being it has a beautiful ethereal melody. However depending on the song played, especially by Vesperus this flute can be extremely dangerous due to being able to entrance like a siren at sea. If the wrong person hears Vesperus playing while he is shepherding souls it can cause hallucinations, madness, and worst case even death. But to the lost, the sick, mothers in labor, people suffering nightmares and grief, and insanity Vesperus's flute can give a moment of comfort. It is due to not only this flute but his lovely, gentle singing voice that has earned him an astounding titles as he grew and matured. Vesperus and his Equinox Flute, depending on the person and their views it is a sacred treasure or even the reverse. But to those saved and helped the melodies heard from this flute is the stuff of dreams.