Volume 4 covers chapters 26 – 34 in the manga.
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Synopsis: 
Tanjiro sets out on the path of the Demon Slayer to save his sister and avenge his family!
In Taisho-era Japan, kindhearted Tanjiro Kamado makes a living selling charcoal. But his peaceful life is shattered when a demon slaughters his entire family. His little sister Nezuko is the only survivor, but she has been transformed into a demon herself! Tanjiro sets out on a dangerous journey to find a way to return his sister to normal and destroy the demon who ruined his life.
After a fierce battle with a demon inside a maddening house of ever-changing rooms, Tanjiro has a chance to find out about the fighter in the boar-head mask. Who is this passionate swordsman and what does he want? Later, a new mission has Tanjiro and his compatriots heading for Mt. Natagumo and a confrontation with a mysterious and horrifying threat…
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Number of pages: 192
Release date: January 2019
Age rating: 14+
Number of volumes: 23 (completed)