A new genus, Gesasha Abdel-Wahab & Nagahama, and three new species therein are described and illustrated from Gesashi mangroves, Okinawa, Japan. Molecular phylogenetic analyses of the partial SSU and LSU rDNA placed the three new species into a clade distantly related to morphologically similar fungi with a high statistical support in the Halosphaeriales, Sordariomycetidae, Sordariomycetes, Ascomycota. The new genus is characterized by hyaline to light-brown, immersed to erumpent coriaceous ascomata, persistent asci with a thickened apical pore with a cytoplasmic retraction below the ascus apex and uni or bi-celled, globose to widely ellipsoidal ascospores with or without ephemeral, amorphous polar to sub-polar appendages.