The Lunar Sickle is a weapon that can be obtained in Lunar Shadow.
If the player takes Zero's Lament instead, the Lunar Sickle can be found in the Confusion Zone (LS) instead, by solving a puzzle in Servant Quarters RR and entering one of the doorways that are created by the puzzle.
The spell fires a weak Lunar-elemental sickle that passes through walls.
LUNAR SICKLE: a spell that creates weak,
crescent moon sickles that go through
walls. Not to be confused with scythes.