Voadam
Legend
Can you think of a real world mythology where a mortal became a god by usurping a god?But isn't that also part of several settings and real world mythologies, how some hero gained godhood by ursupring a god?
Chronos usurped Uranos's big role and was overthrown in turn by Zeus but none of them were mortals.
Hercules became a god by being raised by the gods at his mortal death by the hydra poisoned shirt, not by killing another god. One myth says Hestia stood down so he could take her place among the Olympians but he did not wrest her place from her.
D&D mythology has a few places of deicide as ascension path and I guess you could go with the Highlander movie as a template, but I can't think of an actual myth off the top of my head that uses killing gods as an ascension model.