WRITTEN BY RIYA DUBEY
The older upper moon 6 which was Daki and Gyutaro were defeated in the entertainment district. After Gyutaro and Daki's defeat, Muzan employed a new upper moon 6.
A demon named Kaigaku was given the position. Before becoming a demon, Kaigaku was a demon slayer and was Zenitsu's senior.
He was a user of the thunder breathing style and trained under Jigoro Kuwajima. Before turning into a demon, he was a demon slayer.
He encountered Kokushibo, the upper moon 2 during a mission and surrendered himself, and turned into a demon.
Kaigaku has the advantage of knowing a breathing style and being able to utilize it. However, in an all-out battle, it is Gyutaro and Daki who would undoubtedly win.
Kaigaku can use a breathing style and he is a very skilled swordsman. Training under the former Thunder Hashira made him quite strong. However, that is not all that is required to defeat Daki and Gyutaro.
Kaigaku was turned into a demon long after Gyutaro. Due to this fact, he is very inexperienced in using his blood demon arts.
Gyutaro is stronger than the upper moon 6. Kibutsuji Muzan himself mentioned that if Daki wasn't holding him back, Gyutaro could've become the upper moon 5. This is why Gyutaro is stronger than Kaigaku.