Excerpt from Esoteric Pilgrimage Destinations of the Gothic Sector, Volume 7, by Adept Matthias Laetorius.
"The Harrow'e'en celebration on Ophatran Secundus coincides with the traditional yearly arrival of the Emperor's Tithe Fleet. Although major functions begin a day before the first voidship docks with the orbital stations above the planet, there are several preparatory stages. The most important ritual observance, which sets the date of Harrow'e'en, is a confluence of officials from the Adeptus Astra Telepathica and the Navis Nobilite. The assembled adepts consult the planet's ancient orrery, and contact the fleet's chief astropath to pinpoint the imminent arrival.
Once the arrival date has been formally announced by the Imperial Governor, and the Bells of Warning are sounded, the citizens of the capitol throng to the shrine district. The multitudes pass through the Crusader Gates and into the Ecclesiastic precinct. Crusaders stand in watchful vigil and priests find positions that carry their voices to the crowds. The people of Ophatran believe that vengeful and malignant warp entities cling to the voidships, and that the veil between the Empyrean and reality are thin on Harrow'e'en. The priests recite horrifying tales of these creatures of the Immaterium, and the prayers to combat them.
The most exciting event, certainly from the perspective of the children, is the day preceding the docking of the first voidship. On this day, most of the citizens stay indoors, and those that venture out are likely to meet with a raucous procession led by ‘Spirits of the Warp’. Children that are able to recite their hymns are allowed to wear outlandish costumes, and they roam the streets seeking citizens for the procession to test.
Anyone targeted and detained by these roaming rapscallions must stop and recite the proper prayers of protection, or suffer chastisement from the Adepta Sororitas that accompany the procession.”