Mitsuri Kanroji and Obanai Iguro vs Nakime

Mitsuri Kanroji and Obanai Iguro vs Nakime is a battle that takes place in the Infinity Castle between the Love Hashira Mitsuri Kanroji and Serpent Hashira Obanai Iguro against Upper Rank Four Nakime. During the end of the fight, Yushiro joins in the fight to aid the two Hashira.

Prologue
While Mitsuri Kanroji and Obanai Iguro wander through the Infinity Castle, Mitsuri comes across a female demon wielding a biwa with a large bachi pick. They both see the kanji for Four on her singular iris and are surprised that Muzan has already replaced Hantengu's position of Upper Rank 4 so soon. Mitsuri comments to herself that Shinobu sacrificed her own life in order to aid Kanao and Inosuke defeat Upper Rank 2, Doma with her being younger as well. This boosts her confidence and her drive to do the best she possibly can against any demon, no matter how strong they are.

Battle
Mitsuri immediately engages the Upper Rank and tries to behead her with presumably a Love Breathing technique but Nakime reflects the attack with her Blood Demon Art: Castle Manipulation to warp a wooden door in between them two. As Mitsuri's sword makes contact with the wooden door, Nakime manipulates to door to push Mitsuri off the edge in order to fall to her death. As Mitsuri falls, she nosebleeds from embarrassment and the backfire of her arrogance. Obanai grabs hold of Mitsuri and brings her to safety on a nearby wooden column. Obanai advices Mitsuri that since they have idea how the Upper Rank's Blood Demon art functions or if she has any other abilities, they should analyze her capabilities and proceed calmly to which she completely agrees. As they advise each other, the "floor" they were standing on opens in order to separate the two Hashira. They both grab the door frame and leap off as more doors open to separate them again. The adjacent columns now move in order to crush the two, while Obanai dodges the columns Mitsuri was distracted for his safety and gets caught by one which rapidly ascends towards a ceiling. Fortunately, Mitsuri was able to save herself by slashing open the column which gave her the opportunity to dodge the crush. Mitsuri wall-jumps off the column and tells Nakime as she knows that she won't be able to hit her with the same exact attack twice. Mitsuri leaps over the wooden door that pushed her off before and sees an opening for her to use another Love Breathing technique in order to kill the Upper Rank. However, Nakime teleports an open door for Mitsuri to fall into which warps her off the column making her fall into an even more treacherous depth. Mitsuri makes a very pouty face at herself because of her being juked again by a similar attack. Obanai attempts to behead Nakime with his Serpent Breathing, Second Form: Venom Fangs of the Narrow Head but the enormous wooden column that she has been merged with quickly ascends and throws Obanai completely off of it. He remarks that Nakime's Blood Demon Art isn't exactly deadly like her fellow Upper Ranks but it is indeed far more frustrating to fight against which makes him fear that their fight will be a very long and troublesome one.

Aftermath
Yushiro takes control of Nakime's vision to shift the rooms in the Infinity Castle outside in order for Muzan to soon be exposed to the sunlight, by covering Nakime's eye with a paper talisman and drilling his fingers into Nakime's skull. Yushiro successfully gets the remaining Demon Slayers and Muzan outside of the castle.