On the subject of Kyuubi, what would be his role in the vaxxing of Kanako? He has to be involved somehow, they're siblings living in the same house. Personally, the whole thing gives me FMA vibes.

Just imagine

Kyuubi had always idolized his father
"Unrecognized genius, the brightest mind of a generation, a dozen generations even" his father's self given titles, but he believed every word of them.
So it was easy for Kanako to talk Kyuubi into it
"Come on Kuwy, you always said you wanted to be just like dad. Well here's your chance."
"I don't know about this Kanako. Mom said-"
"Mom doesn't know about science stuff. She's just scared of what she doesn't understand. Would dad run away just because other people told him something was scary?"
Kyuubi didn't need to respond, he knew that question only had one answer. Dad was brave. He ran headlong into the unknown so he could make it known, while all the other monsters were too scared to look.
Kyuubi nodded at Kanako
She pushed the door open and they stepped inside
The lab itself was dusty and dark, covered with books and rough scrawled notes. Kanako couldn't understand a word of it, but Kyuubi could make sense of some of it.
It was incredibly advanced stuff, but his parents had been very proactive with his schooling, and he had learned a few of the basic concepts from Chujin himself.
From there it wasn't long until he had a working understanding of the research, which he relayed to Kanako in simple terms
The main problem was doing all of this without being caught by Ceroba
As much he wanted to make her proud by showing her he could be just like dad, he knew Ceroba would only understand it after he had shown her the results
Besides, it was all just books, knowledge never hurt anyone. That's what always said.
Eventually they had it, the final part of dad's research. The soul serum. With it, a normal monster could obtain the power of a boss monster.
To produce it, two components were required: an unrefined serum, made from raw soul extract; and a live boss monster host, into whom the unrefined serum would be injected, and from whom the pure serum could be extracted.
The lab had just enough extract to make two doses of raw serum, one for each of them
All they had to do was take the plunge, inject the syringe, and they'd accomplish everything dad had given his life trying to achieve
"Kanako, I'm scared."
"Stop being such a baby Kuwy. We've come this far, read all the books, done all the work, now its just time to finish the research. Then we'll finally be able to make dad proud."
"But that was different. That was just reading, learning. There's no harm in knowledge. This is real testing, on ourselves. We could get hurt... I-I thing we should stop, Kanako."
"After all this? Come on, don't you want to be a hero? To save everyone? To make dad's dreams come true?"
Kyuubi didn't respond.
"Well fine, be a baby. I'm gonna be a super hero."
Kanako took a syringe, and looked at it
She held out her arm, and hesitated for a moment, then slid it in
She winced as she felt the needle break her skin
Kyuubi shut his eyes, too scared to watch
...
"See, I told you it'd work."
Kyuubi opened his eyes to see Kanako standing in front of him, perfectly fine.
"Wow, i-i-it actually worked."
"Of course it did. Its dad's research" Kanako replied
Kyuubi felt his heart leap in his chest. He did it, he actually did it. If only dad could see him now.
"Now what do you say? Still too scared to try it?" Kanako asked
"I-I'll do it."
He reached for the syringe, but stopped when his eyes caught sight of the needle.
"Could you... do it for me?" he asked, knowing all too well he'd flinch too much if he tried to inject himself
"Sure, you big baby." She chided playfully
Kanako reached out for the second syringe, but her hand kept going past it.
Then past the table.
Then continued all the way to the ground as she face planted on the floor
"Kanako!"
Kyuubi rushed to his sister side
"Kanako! Are you ok?"
...
He tapped her shoulder
"Kanako!"
...
He shook her
...
"KANAKO! KANAKO, PLEASE SAY SOMETHING! WAKE UP, PLEASE!"
He shook her again
...
No response
With no options left, he did the only thing he could think of
"MOM! MOM! HELP!"
The rest of that day was a blur
He remembered Ceroba coming downstairs, finding him as a sobbing mess on the floor, Kanako lying next to him unresponsive
He remembered the rush to the hospital
The shouting, the crying, the wait in the lobby
The painful failed explanation which Ceroba understood all too well anyways
And worst of all he remembers the look on her face
Not fury, not horror, just a sad look of acceptance