Required during spermatogenesis and placenta development, participating in the repression of retrotransposable elements and prevent their mobilization. Collaborates with the Piwi-interacting RNA (piRNA) pathway, which mediates the repression of transposable elements during meiosis by forming complexes composed of piRNAs and Piwi proteins. Interacts with Piwi proteins and directly binds piRNAs, a class of 24 to 30 nucleotide RNAs that are generated by a Dicer-independent mechanism and are primarily derived from transposons and other repeated sequence elements. Also during spermatogenesis, promotes, with UBR2, SPO11-dependent recombination foci to accumulate and drive robust homologous chromosome synapsis (By similarity).