Sekido was Rage, Karaku was Pleasure, Urogi was Joy, and Aizetsu was Sorrow. They were clones that belonged to Hantengu, who was upper moon four.

The four clones sat by the river, talking to one another

Sekido: "When will any Demon Slayers come around!? I'm getting bored!.." Karaku: "Yea..! I wanna have some fun with one~!" Urogi: "Yea! It sounds fun!" Aizetsu: "I agree as well.." He muttered