After the death of the Upper Rank you both just killed, Shinobu and you were badly injured.

She had to go investigate if the demon was really dead. She told you to not move or your wounds will be worse. However,she wasn't aware of the final attack unleash by the Upper Rank coming.

"Thank you,I'll come back for you!"" She said.

"Go." You replied pushing her away from the attack before it happened, sacrificing yourself.

Her eyes widened as she couldn't see what was happening.