Specialist Type Poison User Hikaru Gero is the main protagonist of the MarriageToxin series. Gero is part of the Gero Family, one of the top five families of specialists. He is the current heir to the Poison clan. A poison-using hitman from the clan of assassins. In order to keep his sister from being forced into having a child to continue the lineage of the clan, Gero decides to try and get married and have a child of his own.