With the massacre of Yoriichi's students complete, Michikatsu made his way to the Ubuyashiki Estate next, reaching there about an hour after he had met with Muzan. Two skaters who had been standing guard near the front entrance were already dead, their throats slit and their chests and abdomens stabbed many times by him as he entered into the yard of the estate.
Having heard the commotion outside, Shiro's wife, Ayako, ran out with a katana of her own and yelled, "What's going on out here?! Who's there?!"
Michikatsu drew his sword in response. "It's me."
"Wait… Tsugikuni-san, what are you doing?!" Michikatsu did not answer her, and instead attacked. Ayako fought him off with her sword initially, the two sparring out in the yard and him unable to land a hit on her due to her past as a slayer before she married Shiro. "Why?! Why are you doing this?!"
"Because it's my destiny," he replied before he managed to land a hit on her shoulder, slicing it and causing her to wince in pain. "Take that!"
"Damn it," she yelled in frustration and pain. "Stop this madness already!"
"This isn't madness," Michikatsu yelled back before stabbing her in the stomach with his sword, stopping her dead in her tracks. "This is just my duty to my master."
"Your… Your master?" Blood poured from her mouth as she began to cough it up due to her soon to be fatal injuries.
"I am no longer Tsugikuni Michikatsu," he told her as he pulled his sword out of her, leaving her on the ground to die of blood loss. "I am Kokushibo, loyal servant of Kibutsuji Muzan. Tsugikuni Michikatsu is dead!" He then turned to the house, where he saw Shiro standing on the front porch in shock. "So… Oyakata-sama, we now meet as enemies."
"What the fuck did you do to my wife?!" Shiro was enraged as he grabbed a naginata hanging on the wall behind him. "You bastard!"
Michikatsu sighed and charged at him, declaring, "Breath of the Moon, First Form: Dark Moon, Evening Palace!" Despite Shiro trying to deflect him, Michikatsu slashed his head off in a crescent-like horizontal motion, killing him instantly. In one instant, he crippled the entire Demon Slayer Corps by murdering its leader. "Now they're finished…"
…
Half an hour later, Yoriichi and Sora were walking around the blood-stained house of the Ubuyashiki Estate. The two were sickened by what they found: Michikatsu had not only murdered Shiro and his wife, but also all but one of his six children, leaving only a five-year-old son alive. He had also murdered two slayers and a servant of the family, making the total death toll of his rampage now sixteen people, with possibly more to come. Sora asked Yoriichi as the two stared at the lifeless body of a young girl, "Where did his wife go? She was just with us earlier."
"Tenko left to confront him," Yoriichi replied with a sigh. "I warned her against it, but she didn't listen."
"I'll go find he-"
"No," Yoriichi insisted.
"Why not?"
"I'll do it," Yoriichi replied as he turned away from him. "I have a feeling I'll find my brother too when I find her. I'll take care of him. As my older brother and as one of my former students, he's my responsibility, so I need to hold him accountable for what he did."
"At least let me come with yo-"
"Again, no." Yoriichi then left on his own. "This is my mission, and my mission only. Stay here and protect the Oyakata-sama's last surviving son. He's our only hope."
…
An hour later, Michikatsu was standing just outside the village of Taiwa, his clothes stained with blood and his sword coated in red. He had gone through and started massacring random people in their houses, but had stopped a few minutes prior as he waited for Muzan to eventually arrive and find him. His total body count was now thirty-five, and he wanted to add more, but knew that Muzan would soon find him. He said to himself as he cleaned his sword with a piece of cloth, "I wish I could go on longer…"
"Michi! Michi! MICHI!"
"Huh?"
He turned around to find Tenko running towards him, clearly in a state of distress. "Michikatsu!"
"Wait," Michikatsu then said to her. "You found me?! How?!"
The two then embraced each other in a tight and emotional hug, Michikatsu even twirling her around before setting her down. "Hey."
"What are you doing out here?"
"I was so worried about you," Tenko told him. "Yoriichi said horrible, horrible things."
His smile turning into a look of discontent, he asked her, "What things did he tell you?"
"He said you murdered his students and killed the leader of the corps," Tenko told him. "Is it true?"
Not answering her question, he told her, "My brother is trying to turn you against me, Tenko. I won't let him."
"Michi, he cares about us. All he wants is to see us happy, and all I want is you and our children. I need your love, Michi."
Michikatsu replied to her, "Your love alone won't save us. Only when I become a demon will I be able to keep us safe forever."
"At what cost?!"
"I lost you once due to my own stupid mistakes," Michikatsu told her. "I won't lose you again. Once I become a demon, I'll be more powerful than any demon slayer has ever dreamed of. Muzan even offered to give me some concessions and freedoms not seen in other demons so I can be by his side, and one day, I'll become so powerful I can even overthrow him."
Tenko by now was desperate. "Please, run away with me and our sons. We can forget everything that happened and start a new life. There's still some good in you, Michikatsu."
"Don't you see? We won't have to run." Michikatsu smiled as he told her of his ambitions with a small hint of worry in his voice. "If I can overthrow Muzan one day, I can also overthrow the emperor and all of the clans that rule this country. I can unite Japan under me, and we can be safe forever while we make things the way we want them to be. I can even demonize you and our children, and we can live forever as the rulers of Japan."
Tenko was horrified to hear of Michikatsu's ambitions to take over her country and unite it under his dictatorial rule. "No…" Tears streamed down her face as she realized he had truly changed for the worse. "No, please… This can't be real… You've changed. Yoriichi was right about you."
"Enough about my stupid brother," Michikatsu demanded of her. "I won't let you turn against me."
"I don't even know who you are anymore," Tenko cried. "You're not the man I fell in love with and married. I can't follow you."
"Because of Yoriichi?"
"Because of you, damn it!" Tenko was now yelling at him. "You're going to destroy Japan if you do this! You'll kill everybody you know and love!"
"Tenko! Tenko! What's going on?!"
Michikatsu saw that Yoriichi was coming in right behind Tenko and got incredibly angry with her. "Did you bring him here?!"
"What?! No!"
"LIAR!" Michikatsu then pushed her to the ground. "You brought him here to kill me!"
"I didn't!"
"I don't believe you!" Michikatsu then grabbed her by the neck and hoisted her up into the air, strangling her.
Yoriichi was horrified to see Michikatsu strangle his own wife and beckoned to him, "LET HER GO, NII-SAN!" When he refused to do so, he told him again, "Let. Her. Go."
"Fine," he replied as he dropped her to the ground after having strangled her to the point of unconsciousness. He looked at his own brother with hatred in his eyes and yelled, "You… You bastard! You turned her against me! My own wife, the mother of my own fucking children hates me because of you!"
"You've done that yourself," Yoriichi corrected him.
"I won't let you take her from me!"
"Your lust for power has already done that."
Michikatsu warned him, "Don't make me fight you, brother! Go away!"
"I cannot do that," Yoriichi replied. "You allowed our sworn enemy, the man who has caused so much suffering all across Japan, to twist your mind, nii-san. Now, you've become the very thing you swore to destroy."
"Fuck your lectures," Michikatsu spat back. "They won't work on me. I did all of this to make sure my family would be safe."
"That isn't the only reason," Yoriichi told him, inferring there was something else going on. "I know you."
"You know nothing about me!"
"Tell me the other reason, nii-san!"
"I want to be more powerful than you," Michikatsu finally admitted. "There, I said it! I was the older twin, and yet you surpassed me! Everyone always thought you were the older one whenever they met us, Yoriichi!"
Yoriichi was almost at a loss for words. "So… So you let your desire to surpass me lead you down this path?!" He thought to himself, "He was jealous… Of me?! How?!"
"Enough," Michikatsu cut him off. "Because of my actions today, and because of the actions I will soon take, I will be able to bring true peace to the divided and fractured lands of Japan, and my family will be able to reshape it, if not the whole world, in our image! I will be more powerful than anyone!"
"What? How… Muzan is clearly bullshitting you!"
"Muzan has nothing to do with that desire. One day, I could surpass him."
Yoriichi was dumbfounded. "Muzan won't let you rebel against him. He'll just kill you if you try!"
"He will never know of my desires," Michikatsu insisted. "Now, don't make me kill you, brother. You're my enemy if you're not on my side."
"Nii-san," Yoriichi said as he realized that a fight was now inevitable, as much as he would have preferred to not do it. "I… I'll do what I must." He then pulled his sword out.
As Michikatsu pulled his sword out, he warned him, "You will try." As soon as he finished speaking, he jumped up and lunged at Yoriichi, who quickly blocked him as their swordfight began.
As Yoriichi and Michikatsu continued to trade blows, the former thought to himself, "I can see true evil in his eyes. This is not my brother. My brother, as far as I'm concerned, is dead. This man in front of me has killed him." Yoriichi nearly fell into a creek behind him before he regained his footing and continued to deflect Michikatsu's blows.
As he turned away from the creek, Michikatsu kicked him away and then declared, "Breath of the Moon, Third Form: Lonesome Moon, Chains!" He then unleashed many rapid slashes into the air, blowing Yoriichi back further. "How about that?!"
"Breath of the Sun, Sixth Form: Solar Heat Haze!" Yoriichi made a horizontal slash in the air that seemingly missed, but instead actually hit Michikatsu, who was just barely able to deflect it while still suffering some small cuts from the attack. "I have failed you, nii-san," he admitted to him. "I have truly failed you!"
Michikatsu ignored him and attacked again, the two once again exchanging blows and deflecting each other. Then, after kicking Yoriichi again, he began to choke him by grabbing his neck with one hand. As he tried to push him to the ground, he gave him a smile and told him, "Goodbye!" However, Yoriichi was able to kick Michikatsu off of him and force him to let go of his grip, and the two once again traded blows with their swords.
Eventually, the two stumbled into the creek, with Michikatsu falling into the water face-first and coughing it up as he got up and grabbed his sword again. Yoriichi declared to deflect his attacks, "Fourth Form: Burning Bones, Summer Sun!" This attack saw him use a large circular slash of his sword, pushing Michikatsu back a few feet.
"Fifth Form: Moon Spirit Calamitous Eddy!" Michikatsu then made multiple curved slashes with his sword, barely missing Yoriichi's neck by just a few inches and managing to graze his cheek.
"Eighth Form: Sunflower Thrust!" Yoriichi tried to thrust his sword directly into Michikatsu, but he was able to not only deflect the attack, but also kick him in the stomach, knocking him down again and knocking his sword out of his hand. Just before Michikatsu could strike him down, he was able to grab his sword and then hold him at bay. "I meant it when I said I failed you!"
"When I become a demon," Michikatsu told him. "My family will be safe!"
"Muzan is lying to you! Why don't you see it?!"
"He has the power to save them," Michikatsu retorted. "He wouldn't lie about that knowing how much of an asset I would be to him!"
Frustrated with his denial of what seemed to be a simple fact, Yoriichi yelled, "Then you are truly lost!"
"This is the day you will die, Yoriichi." Michikatsu then attacked him again, but this time, Yoriichi was able to not only deflect him, but also manage to climb back onto dry land. "You won't get away that easily!" He tried to jump onto dry land with him, but slipped and fell into the water again.
Due to the change in elevation being about three feet, Yoriichi was now staring down at his brother. "It's over, nii-san! I have the high ground!"
Michikatsu remained defiant, yelling back, "You always underestimated me! Well now you never will again!"
Knowing that he was about to try to attack him from below by jumping up, and knowing he had a good chance of failing, Yoriichi begged of his brother, "Please, don't do it!"
Michikatsu ignored him and let out a roar of rage as he focused all of his energy into his legs and jumped up, trying to swing down on Yoriichi from above, only for Yoriichi to slash back at him in response and then push him down and back into the creek. As he tumbled into the water, three other objects fell with him: His two legs and half of one of his arms. Michikatsu screamed in pain as he struggled to keep his head above the water with his remaining undamaged limb and his severed ones rolled in alongside him. "Aaaagh, fuck! Fuck, my legs! My arm! It hurts!"
Yoriichi was horrified at what he was forced to do to his own brother to defend himself. He looked down on him as he continued to moan in pain and bleed profusely from his wounds, knowing he would most likely die. All the memories he had of the two of them from birth up to when Michikatsu became a slayer alongside him played in his head as he yelled with tears in his eyes, "We were the chosen ones! We were supposed to destroy Muzan together, not have you join him! Please, nii-san, don't do this to us!"
Michikatsu wanted nothing to do with Yoriichi or his demands. He looked up at his brother with a wild hatred in his eyes as he screamed at him, "I HATE YOU!"
As he was yelled at, Yoriichi grabbed his sword, intending to keep it as a memento to the brother he once had before he turned to evil. He then turned back around to him and remarked, "You will always be my big brother, Michikatsu. I love you."
As Yoriichi walked away, visibly and audibly crying to himself and effectively leaving his own twin brother to die, Michikatsu immediately began to regret telling his brother he hated him, but knew that it was too late to take it back now. His wounds still hurt, so he continued to moan and scream in pain as his vision began to fade in and out due to blood loss. "No… No! Aaaaagh! Help me! Please, help me!"
Yoriichi managed to run to Tenko after the fight concluded. He bent down and checked her body, trying to feel for any signs of life. When he found none, he gasped. "Te-… Tenko… She's dead…" Indeed, Tenko had passed away due to her strangulation, making her Michikatsu's final victim aside from himself for the day. He then picked her body up on his shoulders and walked away from the scene of the battle with it, thinking to himself, "I'm so sorry, Tenko… I couldn't save your husband after all…"
As he left, Muzan managed to find Michikatsu by the creek bank while accompanied by another demon underling. The underling spotted him first, telling Muzan, "Master! Master! He's over here!"
Muzan ran over to find Michikatsu passed out and unconscious from the pain. "He's not awake!" However, when he got into the water and checked him for signs of life, he found them. "Wait… He's still alive, but just barely. I hope this works…" He then took a deep breath and jammed one of his fingers into his back to inject blood into him to start the demonization process. Once this was done, he told his underling, "Get in here and help me get Kokushibo out!"
"On it," he replied as he got into the water and lifted Michikatsu up, leaving his severed limbs behind as he began to slowly come to due to the beginning of the blood injections by Muzan.
