Who is the weakest upper moon?

In Demon Slayer (Kimetsu no Yaiba), the Upper Moons are the strongest demons who serve under Muzan Kibutsuji, the leader of the demon army. They are ranked from Upper Rank 1 to Upper Rank 6, with each Upper Moon having incredible power and abilities that make them formidable opponents to the Demon Slayer Corps. However, despite their overall strength, one of the Upper Moons stands out as the weakest, and that is Upper Rank 6, Kaigaku (later demoted from Upper Rank 6) and Rui, who is considered to have been one of the weakest in his era.

Let’s take a deeper look into these two characters and their ranking as the weakest among the Upper Moons.

Kaigaku: The Fallen Upper Rank 6

Kaigaku is a demon who initially served as a member of the Demon Slayer Corps before betraying his fellow slayers and becoming a demon. He was once the apprentice of Zenitsu’s master, Kanao Tsuyuri, but after he transformed into a demon, he became the Upper Rank 6 under Muzan Kibutsuji.

While Kaigaku’s demonic abilities made him a powerful opponent, his abilities were still far from the likes of other Upper Moons, such as Akaza or Douma. He did not possess the same level of mastery over his demon abilities as other Upper Rank demons, and he lacked the sheer destructive force or unique blood demon arts that could place him in a higher tier.

His main weakness was his insecurity and lack of experience compared to others in the Upper Moon ranks. Kaigaku’s main weapon was the Thunder Breathing technique, but he failed to master the style to the level required to be a true threat. His arrogance and underestimation of others led to his downfall when Zenitsu faced him during the final battle and defeated him in an emotionally charged showdown. This final battle made Kaigaku’s status as the weakest Upper Moon quite clear.

Why Kaigaku is the Weakest:

1. Lack of Unique Abilities: Unlike other Upper Moons, Kaigaku’s abilities were not as unique or devastating as those of other demons. His Thunder Breathing style was effective, but it was not at the same level as some of the more refined and powerful Blood Demon Arts.

2. Mental Instability: Kaigaku’s lack of self-confidence and his reliance on his power rather than his actual skills made him weaker. His tendency to doubt himself led to him becoming unstable, which was evident in his final confrontation with Zenitsu.

3. Defeat by Zenitsu: Despite Kaigaku being an Upper Moon, he was defeated by Zenitsu, a character who had not fully unlocked his true potential. This highlights how Kaigaku was ultimately one of the weakest among the Upper Moons.

Rui: The Former Upper Rank 5

Another character that is often considered one of the weaker Upper Moons is Rui, the demon who previously held the title of Upper Rank 5 before being killed by Kamado Tanjiro and Hashira Kanao Tsuyuri. Rui’s demonic abilities were formidable, and he had control over his Blood Demon Art—the ability to manipulate and control spider threads. Despite his powers, Rui’s rank and abilities were considered somewhat lacking compared to other Upper Moons.

Rui’s main weaknesses included his emotional instability and overreliance on his Blood Demon Art. He became too fixated on his ideal family dynamic, and his lack of control over his emotions led him to make irrational decisions. Additionally, his fight against Tanjiro and the Hashira exposed significant gaps in his combat skills, as he was ultimately defeated due to the combined efforts of Tanjiro and Nezuko.

Why Rui Was the Weakest:

1. Emotional Weakness: Rui's attachment to his twisted ideal of family led to his undoing. He lacked the maturity and focus of other demons like Akaza or Douma, who were much more level-headed in their actions.

2. Defeated by Tanjiro: Rui’s ultimate defeat came at the hands of Tanjiro, who was able to tap into his full potential and defeat him. This battle showcased Rui's vulnerabilities and highlighted his position as one of the weaker Upper Moons.

3. Lack of Physical Strength: While Rui’s Blood Demon Art was powerful, it was no match for the sheer physical strength and combat prowess of higher-ranking demons. He was overwhelmed in combat by Tanjiro and the support from Nezuko and the other Demon Slayer Corps members.

The Conclusion: Weakest Upper Moon

In conclusion, Kaigaku and Rui can be considered the weakest Upper Moons, though for different reasons. Kaigaku's defeat by Zenitsu and his lack of development as a demon highlight his inability to rise to the level of the other Upper Moons. Rui, on the other hand, was defeated by Tanjiro and lacked the emotional and combat strength of his fellow demons.

While both were formidable in their own right, neither of them could match the sheer strength and power of Upper Moons like Akaza, Douma, or Kokushibo. This makes them the weakest links in the Upper Moon hierarchy and provides a sense of relative power in the Demon Slayer world.

Despite their weaknesses, both characters contributed to the overall tension and drama of the series, proving that even the weakest demons in Demon Slayer can leave a lasting impact on the story.