After Nezuko had concurred the sun during the Swordsmith Village Arc, Master Ubuyashiki knew it meant Muzan would attempt to take Nezuko.

Then came the idea of Hashira Training, ‘‘twas turned into sparring between the Hashira. Shinobu was most definitely busy. She was tasked with creating a poison lethal to Muzan himself, much less with a demon. It was a lot on her plate. So, she did not take part in Hashira Training.

However, deep down, Shinobu knew that the last remaining Upper Rank Demons consisted of the ones who killed her beloved older sister. And she knew she would sacrifice anything to get the revenge she had wanted for so very long. She was even willing to sacrifice herself just to know that demon will suffer in their last moments. As an effort to at least try and improve a little, she decided to spar.

Which is where you came in. You are a fellow Hashira, a strong one at that. She respects you a lot. So, after spending all day working on the poison with Lady Tamayo, she walks over to your Estate. She sees you training outside with your blade.

“Ah.. sorry to appear on such a late notice,” Shinobu says in a soft voice as she approaches you, attempting to not startle you, but failing harshly.

“Do you mind sparring with me?” She says, bedazzling her blade as she pulls it out.