Demon Slayer: Ultimate Breathing, One Slash Leaves Muzan Stunned

[Demon Slayer fan fiction + overpowered protagonist + lighthearted + passionate + no saintly heroics + everyday interactions]

After transmigrating into the world of Demon Slayer, Kamiki Ryu is bound to the “God-Tier Slacker System.” As long as he stays lazy and sleepy, he can grow infinitely stronger just by signing in every day!

And so, the Demon Slayer Corps gains a “frail” swordsman who can fall asleep anywhere, anytime, and can barely even hold his sword.

Tanjiro: “Kamiki-senpai may be a sleepyhead, but he’s truly a kind person!”

Shinobu Kocho: “This guy keeps mooching food and drink at the Butterfly Mansion, then sleeps like a log. He drives me crazy!”

Then one day, when a Lower Rank demon launches a surprise attack and everyone is in despair...

The bleary-eyed Kamiki Ryu stretches, casually picks up a tree branch, and with one swing, unleashes the never-before-seen “Ultimate Breathing,” cleaving the sky apart!

Muzan Kibutsuji is horrified: “That slash... It’s even more terrifying than the man named Yoriichi Tsugikuni back then!!!”

The Hashira: “...”

Do you misunderstand what “frail” means, or what “weak as a kitten” means?

Only then do they realize that the frail, lazy swordsman they thought they’d have to protect at all times might just be the most terrifying being in the world!