The next morning, Ryou received a letter from Tamayo about her recent discoveries and thanked him for providing the blood of Upper Moon demon Akaza, which had a high concentration of Muzan's blood.
She explained her analysis: 'Nezuko's blood is changing rapidly and has the potential to conquer the sun. And, it may happen very soon.'
She urged Ryou to keep Nezuko hidden from demons' sight, as there's a possibility Muzan will come to find out about her through the demon blood connection.
If Muzan discovers her trait, it would spell disaster, and there's no telling what he would do to get her.
Reading her letter, Ryou shook his head and wrote his response.
"You're too late, Tamayo. Nezuko has already conquered the sun. Muzan knows about it. You know what this means: the battle between humans and demons is coming.
Humanity needs your help, Tamayo. It's time for you to come to the other side. If you combine your knowledge with Shinobu, who has mastery in the medical and pharmaceutical fields, you could make significant progress in your research.
With your connection to Tanjiro, the Demon Slayer Corps may already know your existence; they will eventually discover your location and invite you to join them. When that happens, accept it.
If they don't reach out soon, I'll personally explain your situation to Ubuyashiki. Don't worry about your safety, no one will do anything to you with me here!"
After sending the letter, Ryou set off from the Nature Manor to attend the emergency Hashira meeting summoned by the Ubuyashiki family.
---
The Next Morning,
The Hashira gathered at one of the Ubuyashiki mansions for the meeting. When Ryou arrived, he saw Kanae, Giyu, Mitsuri, Muichiro, Gyomei, Kyojuro, and Tengen already present. Sanemi and Obanai were the only ones missing.
A few minutes later, Sanemi and Obanai arrived. "So, we're the last ones, huh?" Sanemi muttered, sitting down casually, unfazed by his lateness.
"Sorry for keeping you all waiting," Obanai apologized, taking his seat.
"No problem. Well done on your mission!" Gyomei commended them for their efforts.
Once settled, Sanemi turned his gaze to Mitsuri and Muichiro. "So, you two really fought Upper Moons? For real?"
Mitsuri nodded enthusiastically. "Yup! They were incredibly strong. I thought I was done for, but somehow we managed."
Muichiro simply nodded, "Yes."
Sanemi sighed in frustration, "I'm jealous. Why haven't I encountered any Upper Moons?"
"It feels like almost everyone's run into one," Obanai added, before asking, "Are you both alright? How are your injuries?"
Mitsuri's face brightened, "Oh! I'm much better now, thank you for asking." Her cheeks flushed slightly, her heart fluttering. 'He's worried about me,' she thought.
Muichiro, in his usual calm tone, responded, "I'm better, but I haven't fully healed yet."
With his hands gently clasped together as though in prayer, Gyomei said. "I'm relieved nothing happened to you both, even though you encountered the Upper Moons."
Kanae, noticing their conditions, added, "It's good to see you both recovering well, but it seems your wounds healed quickly. It's abnormal. Shinobu is concerned about the unusual rate of recovery.
If you feel anything off, consult with her immediately." Both of them nodded.
--
The meeting began with the arrival of Amane Ubuyashiki, Kagaya's wife, accompanied by two of their children. She bowed deeply before addressing the gathered Hashira.
"In today's Hashira meeting, I am here on behalf of Kagaya Ubuyashiki. I deeply apologize for the fact that Master Kagaya will no longer be able to appear before you due to his worsening health.
As you are all aware, a demon who can withstand sunlight has now emerged—Nezuko Kamado. Muzan will definitely come for her, trying to conquer the sun too. A large-scale war is now unavoidable."
Amane then turned her gaze toward Mitsuri and Muichiro, her expression calm and inquisitive. "During your battles with the Upper Moons, I was told that both of you manifested unique marks on your bodies.
I would like to hear more about them—under what circumstances did these marks appear? Is there any way to awaken them?"
Unlike Mitsuri's blunder of attempting to describe her experience with a string of vague gestures and sounds, Muichiro calmly recounted how his demon slayer mark awakened in detail—during a near-death struggle.
After that, the Hashira meeting went as happened in the original timeline, with Amane explaining the origin and history of the Demon Slayer marks.
Ryou remained silent throughout the meeting, just sitting there absentmindedly without even listening to the conversation.
Soon, the Hashira meeting ended, and Amane Ubuyashiki bowed once more before leaving with her children. Just as the Hashira were preparing to leave, Gyomei stepped forward and stopped them, proposing his 'Hashira Training plan' to prepare the Corps members for the upcoming battle.
Everyone then spent another hour discussing the specifics of the training program—working out the schedule, time periods, and dates. Each Hashira would take charge of a particular training session, with Ryou overseeing reaction and perception training.