Males pursuing alternative reproductive tactics (ARTs) face uneven sperm competition risk and often invest differently into ejaculates and mate acquisition. In loliginid squids, the existence of two fertilization sites in females (buccal membrane vs. oviduct opening), associated with ARTs, might even raise such asymmetries. By using a privileged site, consorts are predicted to monopolize paternity, making it difficult to understand how sneakers persist along generations. By controlling spermatophore attachment sites used by males, we empirically evidence that fertilization sites indeed influence male reproductive success, with consorts monopolizing paternity when competing with sneakers. However, we also show that females store sperm from several sneakers, which are often used to fertilize part of their progeny, even after recent mating with a consort. Our results not only highlight the importance of the buccal sperm storage organ for sperm provision and offspring genetic diversity but also explain how sneakers might persevere in a system dominated by consorts. Together, these results indicate that loliginid ARTs reflect complex fertilization dynamics, with consorts displaying agonistic behaviors to control paternity, and sneakers mating promiscuously to assure cumulative reproductive success – enhanced by long-term sperm storage. Ultimately, these results highlight the importance of considering fertilization environments when studying ARTs evolution.