When Chinatsu saw Tanjiro take out so many test tubes filled with her blood, she quietly withdrew her arm.
Once Tamayo recovered from her surprise, she cradled the test tubes filled with Chinatsu's blood as though they were priceless treasures, her eyes bright and intent.
Tamayo: "Th-this much! How many experiments could I run with all this?"
Tamayo's eyes sparkled brilliantly, and she nearly lost her composure... no, she had already lost it. At least, Yushiro had never seen her like this before. Still, no matter what she looked like, Lady Tamayo was always the most beautiful person in his eyes.
Tamayo had reaped a rich harvest without even leaving her home, while Chinatsu and Tanjiro quickly departed her residence. Whether Tamayo finished her current research or ran into a problem, she could come find Chinatsu.
If anyone asked who the greatest MVPs of the battle in the Infinity Castle were, the answer had to be Tamayo and Shinobu Kocho, the two women who developed the ultimate poison that could age Muzan.
In the original story, it took their combined efforts to formulate that ultimate poison. In the world Chinatsu had changed, it remained just as indispensable.
Chinatsu was not Yoriichi Tsugikuni incarnate, much less a monster who surpassed him... at least, not yet.
Muzan was powerful. Even after being afflicted with the ultimate poison, his strength remained far above Kokushibo's, let alone when he was at full strength before being poisoned. That ultimate poison was therefore essential to age and weaken him.
Chinatsu and Tanjiro walked through the night, concealing themselves as they returned to the Demon Slayer Corps Headquarters.
The "human" side was going all out to improve its fighting strength, but the "demon" side was going all out as well.
After Kokushibo's death, Muzan issued an ultimatum