Jujutsu Kaisen
Both are modern shounen hits about trained fighters hunting supernatural threats while using visually distinct techniques. Jujutsu Kaisen is more urban and sarcastic, but the squad battles, tragic monsters, and high-end animation make it an easy rec.
Attack on Titan
The connection is the life-or-death war against man-eating monsters and a protagonist driven by family trauma. Attack on Titan is more political and brutal, but fans of Demon Slayer's desperation and monster-hunting stakes often understand the overlap.
Dororo
Dororo shares the historical-feeling setting, demon enemies, wandering structure, and emotional focus on a young protagonist marked by violence. It is less flashy than Demon Slayer, but the tragic demon-slaying journey feels close.
Bleach
Bleach is a common rec because both involve sword-based supernatural combat, stylish forms, and enemies with distinct abilities. Demon Slayer is more compact and emotional, while Bleach is longer and more power-system heavy, but the sword-fighting appeal carries over.
InuYasha
InuYasha shares demon hunting, a historical Japanese atmosphere, travel-party adventure, and emotional conflicts with demons who are not always simple monsters. It is more romance/adventure oriented, but the folklore-action overlap makes the rec make sense.