Several veiws, depends on who the reaper is to you. The first legend of the modern "Reaper" who carries a syth, was started in Europe dureing the back plague. Men in dark robes with terifying faces were seen on the outscrerts of town, waveing "syth like objects" wich would emit a fog. This fog was believed by many to be the real black plague, and were these were seen, the back plagye would soon break out. So if these are who you consider "reapers", then thier syths are/were supisidly made to release a deadly poison. This is simplya legend, could be true coud be false. Many people say aliens, some say creatures from hell, ect.. If I have made any errors, please, do not hesitate to correct me, but this info is correct as far as I know. Personaly, I think the syth has stuck around into the current erra becuase it is a deadly weapon, that could decapitate or cut you in half quickly (thus symbolizing the swiftness of death)
Depictions of Reapers can vary by culture, but they usually wear dark ceremonial clothes and were naturally associated with symbols of Death. Actual Reaper spirits don't really match the typical depictions, but when you've seen one you can understand where some of it came from. While the skeleton is obviously just a symbol of death, as are the weapons they may carry,the cloak and grim appearance are pretty spot on with the darkness around them and the Death Essence(energy).