Complex sentence: Though his dear friend Sayoko Fukasawa warned him in vain, Tachibana shrugged it off until he learned that Isaka murdered Sayoko for meddling in his affairs, overcoming his fear while defeating the Peacock Undead and sealing him.
Split into simpler sentences: Though his dear friend Sayoko Fukasawa tries to warn him, Tachibana does not listen until he learns that Isaka murdered Sayoko for meddling in his affairs. Tachibana overcomes his fear while defeating the Peacock Undead and sealing him.