The origin of the charged hypermultiplets in the six dimensional duality between F theory and heterotic string is found from a purely type IIB string viewpoint through a detailed study in the case of SO(10) gauge symmetry. At each intersection point of zero loci of the discriminant, J function is used to determine the [p,q] charge of an intersecting 7-brane. It is equated to an asymptotic charge of string junctions, which reproduce the expected representation. In relation to the Cartan deformation, agreement with the Het/K3 spectrum is also found for all the other cases of simply laced gauge symmetry.