The ghost of Adina Astra's lover is the sole motivation for Astra heading to the Forest and thus enacting the events of Lost Constellation in the first place.

Lost Constellation

Adina was traveling to the Frozen Lake in order to have a chance to see the ghost of her lover. As Adina travels on the icy surface, the ghost appears right behind her, completely invisible barring their reflection. Adina is pleased to hear the voice of them, and they talk, as the ghost reveals that the Ghost Star does indeed exist, as part of the "Lost Constellation", which Adina gets to witness. Eventually, the ghost dissipated permanently, returning to wherever the souls of the dead go.