Function: ATP-binding RNA helicase required during spermatogenesis (PubMed:28536242). Required to repress transposable elements and prevent their mobilization, which is essential for the germline integrity. Acts via the piRNA metabolic process, which mediates the repression of transposable elements during meiosis by forming complexes composed of piRNAs and Piwi proteins and governs the methylation and subsequent repression of transposons. Acts downstream of piRNA biogenesis: exclusively required for transposon silencing in the nucleus, suggesting that it acts as a nuclear effector in the nucleus together with PIWIL4.