This is an incarnation berry, they were originally developed as a means of easily feeding the masses and quickly incarnating those within new cities of the Demon Kingdoms as it was deemed cruel to leave them unable to find employment or a partner. However, the plant managed to spread beyond the Demon Kingdoms and quickly became seen as a kind of delicious panacea for those who were ageing to once again acquire beautiful looks. Incarnation berries resemble an elongate raspberry coiled in a spiral. Eating these berries will cause a human or any other being to incarnate into a mamonme or incubus.
While it is seen as a panacea, it is also seen as the decadent fruit that can only be eaten once as a human. Once an incarnation berry has been completely consumed the changes begin.
Sweet doom
Pretty much a temptation, a deal with the devil if you wish...
And they kept preaching that the forbidden fruit was an apple...
And insisted that it brought immortality to all who tasted it...
Not realizing they were already dead the moment they gazed upon it...
- Sublaes Liminael, Via Lucis