User blog comment:B214/Chapter 510: Natsu's Heart/@comment-7418318-20161118190331

I wonder if Yukino's debt to Kagura will play any role in the near future. After all Kagura did win the bet and thus Yukino's life does belong to her.

Maybe Yukino will save Kagura's life in some way and that's how Kagura considers the debt payed or somesuch.