Posers

A Poser (Romaji: Pōzā; Kana: ポーザー) is the consequence of being wounded by one of the Arrowheads. It's a materialization of an individual's soul. Therefore, it is an embodiment of an individual. As an embodiment, a poser exhibits abilities and powers that are reflections of the soul that it was materialized from.

However, it should be noted that posers can be "infected" by the "demons" within a devil fruit. If an individual with a poser consumes a devil fruit, the individual's poser will lose its ability and gain the ability of the devil fruit in its place. In addition, the poser will cease to be an embodiment of the individual and become an embodiment of the devil fruit.

Thus, it's impossible to exhibit the power of a devil fruit in conjunction with the power of a poser.

The Arrowheads
Are arrowheads which are composed of naught but artificial viruses named Zero Waters. The Zero Waters were produced by coercing Aibyouka — via torture — into utilizing the Majo Majo no Mi to anthropomorphize a klabautermann and then paying Hugo to utilize the Kyousha Kyousha no Mi to transfer the klabautermann's duality of physicality and spirituality to a genetically modified virus. Subsequently, the virus has been allowed to reproduce into colonies which are clustered into The Arrowheards.

Any living being that is wounded by The Arrowheads will be infected by the Zero Waters. The Zero Waters will alter the living being into having the same duality of physicality and spirituality that both is possessed by them and was possessed by the klabautermann that was sacrificed to create them. This will bestow upon the infected the ability to materialize their soul into a physical form at will.

HOWEVER, because of the duality of their physicality and spirituality, any damage that is inflicted upon the materialized soul will be inflicted upon their physical body as well. For just as a klabautermann is a spirit and body at the same time. So is a Poser one's spirit and body at the same time.