When the stars align for us

Chapter 6

'Kyojuro Rengoku and Mitsuri Kanroji have defeated Upper Moon 3!'
The crow informed all the Hashiras in turn.
When she heard the news, Shinobu was in the town square with Kanao, taking a break from training the three Mizunotos, who had helped with the fight in the Mugen Train. Beyond happy, she hugged her younger sister.
...
The rest of the week was jam-packed with missions. Apparently, with the death of one of his strongest pawns, Kibutsuji had begun to take the situation seriously, seemingly letting all demons loose around Japan.
Shinobu finally found a small window of time at the end of the week, which she spent thinking about the war. Ever since her sister, Kanae's death, her heart had been full of grief, anger and a desire for revenge. She had decided to continue on the path of a Demon Slayer, for this sole reason: she wanted to avenge her sister, by eradicating her murderer. She didn't know exactly who he was, except that he was an Upper Moon, with eyes that reflected all the colours of the rainbow. She also knew that he was a glutton who was obsessed with devouring women, more particularly, strong women. But how was she going to defeat such an opponent? If he had killed Kanae, he would kill her as well. After all, she wasn't strong enough to decapitate a demon. And what would her poison do against an Upper Moon? On one hand, she knew that she was no match for him; no one was! Even Rengoku had needed help to defeat an Upper Moon. But she had to do it on her own...she wanted to do it on her own and that was what she would do. But how on earth would she do it?
Her thoughts were suddenly interrupted by Aoi walking into her study.
'Excuse me, shihan. One of the Kinoes we let out yesterday seems to have had his arm bitten off by another demon. He's unconscious,' Aoi quickly informed her.
Shinobu rushed out of her room, towards the infirmary.
...
After treating the wounded slayer, she asked her student to notify her when he woke up. Making her way back to her study, she resumed her previous line of thought.
So, as much as I hate to admit it, there's no way to finish that monster off with poison. On the other hand, I could give him a large amount of poison to weaken him enough, so that the next person to come across him can finish him. But how can I insert such a large amount into his body?
She heard the door creak open, as Aoi peered through the small opening.
'Shihan, he woke up,'
Shinobu stood up. In the infirmary, she found the same man she had seen a few minutes before, conscious this time.
'Greetings, Kocho-sama,'
'Hello there' she smiled, sitting on a nearby chair, 'I think you can tell that you're out of danger. But there is something I want to ask you,'
He nodded.
'You've lost your right arm, so how did you defeat the demon? I mean, it would have been nearly impossible to run out of there in the circumstances,'
'Oh, well, you see, while I couldn't use my blade in that position, or even move, I didn't need to! He just fell over backwards and stopped moving,'
Shinobu felt her eyes widen.
'Hmm...when you came here last week, what was your injury?'
'A demon had bitten my upper arm and-'
'The arm that you lost today?'
'Yes, there was poison running through my blood, but....'
Shinobu stopped listening to what the patient was saying, as sudden thoughts started racing through her head.
The demon digested the man's arm, had a minuscule amount of poison and yet he died. What if I drank enough wisteria poison every day to fill my body with it? Then, once that monster has devoured me, it will be severely weakened. Anyone could finish him afterwards. Yes, I'd have to give up my life, but revenge is more important.
'Shihan?'
'Yes?' she answered, startled.
'Are you alright?' Aoi asked, squinting at her face.
'Hmm? Oh, fine, thanks,' she replied, ruffling her student's hair.