Unlike the Lycanthrope and Hourai who try to co-exist with nature, Leafer are humans that have been completely taken over by the plants. They are considered to be a long-lived species in general as full assimilation requires a long amount of time.
Because they can photosynthesize, they don't need to eat food. Also, as their brains are taken over by the plants, their personalities become extremely cheerful and mischievous. As a result, they spend their very last moments, before entirely becoming a plant, with an optimistic smile. While most of them spend their days playing pranks, there are some who do real damage, such as destroying the farming fields of the Lycanthrope.