Complex sentence: In her "Deception" ending, she fulfills her duties to Onaga, but then kills him while he is distracted by his victory, therefore becoming the most powerful being in the realms.
Split into simpler sentences: In her "Deception" ending, she fulfills her duties to Onaga, but promptly seizes an opportunity to kill him as he is distracted with his victory. She succeeds, killing Onaga and becoming the most powerful being in the realms.