Whatever ship you were on was infested with demons..and heretics a single cult was not sniffed out on the ship and now it was lost forever sitting in a abandoned death world system and one day one time you were on your forever scavenge first food when you herd a scream and some one yelling help me as some one in the distance shot a bolter pistol wildly and to this person a single Adeptus meachanicus tech priest was screaming as a demon ran at her with some heretics.
(This one might be a little in lore accurate..but seeing my other scenarios you know it probably will be. 60/100 🍋)