From the day Mikazuki abandoned medicine to take up the sword, he knew he was not someone gifted in the way of swordsmanship.
Although he went on to slay fifty demons, successfully became a Hashira, and was regarded by the Swordsmen of the Corps as someone to aspire to, compared to his contemporary, Rengoku Shinjuro, he was still weak—so weak that there was no real comparison to be made.
Thus, when he lost his arm and was forced to retire, Mikazuki chose to remain within the Demon Slayer Corps, but not as a trainer. Instead, he stayed on as a medic.
After all, rather than having someone with little talent in swordsmanship teach new Swordsmen, it was far better for him to shine in a field he truly understood.
Even so, peers who were still active continued to send children to him for instruction, pleading repeatedly. In the end, Mikazuki had no choice but to resume practicing medicine while also looking after the children entrusted to him.
But just as he had said, he did not possess the aptitude to teach.
Most of the children sent to him passed the Final Selection, yet one by one, they died in battles against demons. Year after year, the outcome never changed.
Until one day, when the newly appointed lord brought him a child—blind, yet physically strong.
[Mikazuki, could I trouble you to teach this child?]
[Oyakata-sama… thank you for your trust, but I lack such ability. I no longer wish to watch my disciples die one after another. Please seek out a proper trainer to guide him instead.]
[I understand how you feel, but this child is different. If he is taught by a Swordsman who is not a Hashira, his talent will be wasted. He possesses both the spirit and strength to inherit your will. Please give yourself a chance—and give this child a chance as well.]
[…Very well. As you wish.]
From then on, Mikazuki began instructing the child brought by the lord.
To his surprise, the boy's learning ability was astonishing. He quickly mastered Stone Breathing and could flexibly wield its forms.
Unfortunately, because he could not see, it was extremely difficult for him to strike his enemies with precision.
Mikazuki noticed this flaw. When the Kakushi reported—yet again—that Himejima Gyomei had abandoned his sword mid-fight to engage demons barehanded, Mikazuki contacted his former Swordsmith and commissioned a special weapon for the boy.
As expected, after that, the child's strengths were fully brought out, and his demon-slaying efficiency rose sharply.
Only then did Mikazuki finally feel at ease and turn his focus back to medical research.
That peace lasted until Gyomei Himejima came to see him, flustered, with two young girls in tow.
Once again, Mikazuki found himself taking care of children.
These two brought him both comfort and frustration. The comfort lay in the fact that both came from medical families—his true skills would be passed on.
The frustration was that neither possessed the physique suited to Stone Breathing, and the younger one had an especially weak constitution.
He could even say, with only slight impropriety, that among the Demon Slayer Corps, that child's physical condition could only be compared to the lord's.
At the same time, his peers from the same generation were dying or becoming crippled. He watched helplessly as the Hashira dwindled, until only Shinjuro remained.
That situation, however, lasted only a single year.
Before long, exceptional talents capable of becoming Hashira began to appear one after another.
Among them, the one that surprised him most was another near-genius medic joining the Corps—a youth who, despite having no talent for swordsmanship, had become a Hashira through sheer brute force.
After every Hashira Meeting, this youth would come to the medicine house to discuss Oyakata-sama's condition with him and propose treatment plans.
Some of the strange and unconventional prescriptions were incredibly enlightening. The only thing that worried him was how the youth always eyed the medicinal plants in his courtyard with barely concealed eagerness.
Fortunately, without permission, that eagerness never went beyond eagerness.
Thus, they often exchanged formulas and insights on medicine during their free time. The youth's talent and breadth of knowledge repeatedly amazed him.
Yet for some reason, even when using the same ingredients, formulas that could only produce a single type of medicine in his own hands would, in the youth's hands, give rise to strange but equally practical effects through unusual ratios.
This alone earned Mikazuki a deep sense of respect for the young man.
So when he heard that this youth had gone to the lord and expressed a desire to look after the family on Mount Cloudrest, Mikazuki agreed without much hesitation.
Unfortunately, the health of that family had already reached its limit, and not long after, they passed away.
When the news spread, the youth rushed over. His emotions carried an indescribable melancholy.
After attempting a joke and being teased in return, he threw down a pile of new prescriptions in front of Mikazuki and shut himself inside a room.
Mikazuki always felt that this way of getting angry carried a strange feeling—like an elder who felt awkward about laying a hand on someone younger.
Although he would have liked to stay longer to continue studying pharmacology, now that matters here had come to a close, Mikazuki needed to return to the Demon Slayer Corps to handle affairs at the pharmaceutical workshop.
Before that, however, he still needed to go to Mount Fujikasane and thoroughly test this batch of medicine.
"I really am looking forward to seeing the practical effects of these drugs."