Recent genome-based evolutionary studies have highlighted introgressive hybridization as a major force on the repeated evolution of adaptive traits. Fishes are well-known for presenting cases of repeated evolution of reproductive modes across lineages. However so far, no study has examined the possibility that such event of repeated evolution might have been facilitated by hybridizations between taxa. Pelvic-fin brooding is a unique reproductive mode known only from medaka fishes (family Adrianichthyidae); while females of most medaka species deposit eggs on plans or other materials without parental care, females of brooder species use oddly elongated pelvic-fins to carry a batch of fertilized eggs until hatching. Previous phylogenetic analyses have revealed that pelvic-fin brooding evolved in two distant lineages within Sulawesi, an island of Indo-Australian Archipelago. The repeated evolution of pelvic-fin brooding could be potentially explained by a) convergent evolution of de-novo origin, b) convergent evolution by ancestral polymorphisms, or c) introgressive hybridizations from a lineage to another. Based on QTL mapping using a cross between a brooder and a non-brooder species, and genomic scanning for introgression among Sulawesi medaka species, we discuss which of the above three evolutionary processes is responsible for the repeated evolution of this unique reproductive mode.