Let's check the rankings of the most powerful demons in the series.

12 Kizuki In Demon Slayer

Lower Moon Six - Kamanue/Kyogai

The weakest member of the twelve kizuki, Kamanue was the lower six and was killed by Muzan in the infinity castle

Lower Moon Five  - Rui

One of the first members of the twelve kizuki to be shown in the anime. He was once a human with a frail body who was promised a healthy body by Muzan. 

Lower Moon Four - Makugo

Not much is known about the lower moon four Makugo. She was among the 4 demons who lost their lives in the decimation by Muzan.

Lower Moon Three - Wakuraba

Just like other lower moons we only see him during his death. Wakuraba was the lower moon 

Lower Moon Two - Rokuro

Rokuro was a part of the twelve kizuki and was only seen once when after the defeat of Rui, Muzan lost all his patience for the lower moons and decided to kill them all.

Lower Moon One - Emmu

After the death of Rui, Emmu was the only one of the twelve kizuki lower moons who was left alive after Muzan decided that he will dismantle the entire lower moons.

Upper Moon Six - Daki & Gyutaro

Daki and Gyutaro were brother and sister who used to run a racket in the pleasure district until one day Daki was killed and Gyutaro was stabbed.

Upper moon 6 - Kaigaku

After the demise of Daki and Gyutaro, Kaigaku was recruited as the new Upper six. He was a former demon slayer and the senior of Zenitsu and also a user of the Thunder style. 

Upper Moon Five - Gyokko

Gyokko is the upper five and a human known as Managi had a strange obsession with fish carcasses and everything related to the dead.

Upper Moon Four - Hantengu

Hantengu was a criminal when he was a human and had killed many people. He was eventually caught and given the death sentence

Upper Moon Three - Akaza

Akaza is one of the strongest members of the Twelve Kizuki and a former martial artist. As a human, he was a skilled martial artist who killed 67 people at a rival dojo.

Upper Moon Two - Doma

Doma was the leader of the Paradise Faith Cult and led his group through which he eventually met Muzan. Muzan impressed by him made him into a demon.

Upper Moon One - Kokushibo

Kokushibo is the Upper Moon 1 as well as the first of the group. He was a fierce swordsman who was also among the first group of demon slayers.

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