Demon Slayer: Sorry, I Can't Breathe

(Demon Slayer × One Piece × Haki × Six Powers)

Thanks for the invite. I just “reincarnated” into Demon Slayer after botching an undercover mission in the Marines, and I'm in hell mode from the start. No System, and my starter pack is “fallen family + frail body debuff.” Luckily, I still have my old tricks: Haki and Marine swordsmanship. Watching these boys and girls fight with nothing but “lung capacity,” all I can say is: your fighting styles need work! So I, a “physical-build player” skilled in Armament Haki hardening and Observation Haki precognition, start cleaning up this world's “bugs” (demons), while forcing all the “bad ending storylines” I can't stand into happy endings. Muzan? So you're the final boss? Let me grind through a few Upper Rank dungeons to warm up first!