In Earthsea, I Exorcise a Noblewoman from the Start

【Cthulhu Mythos + Multiple Female Leads + System + Slow Burn】 The treacherous Sea of Earth is shrouded in darkness. Let your SAN drop too low, and you'll go completely mad. Leon has been in the Sea of Earth for two and a half years when he unexpectedly unlocks an Enhancement System. An ordinary creed is enhanced into the 【Exorcist Bible】. One thought unleashes holy light, banishing evil spirits! A battered copper cross is enhanced into the 【Indestructible Vajra Club】, supremely firm and yang, with nothing able to withstand it! An ordinary expedition ship is enhanced into the 【Mysterious Ship from the Abyss】, improving every attribute across the board! … A beautiful noblewoman tainted by evil, a stunning six-foot-two female captain, and a pair of mermaid sisters all come to him for help... He wins them all over. … Until one day, Leon takes the fully upgraded ironclad battleship out with his entire crew and smashes through the ceiling of the Sea of Earth… (The blurb doesn't do it justice. Read the story itself.)