Reincarnated as a Swarm?!

MC found himself (or herself? They don't even remember that) as a wandering soul unable to sense anything, when suddenly an Automatic Reincarnation System told them they died by mistake. What the hell?! Among the different species they cound reincarnate, there was a "Special species". A Swarm... A Swarm?! Out of curiosity, and thinking it was a promising option, they chose this one.