User blog comment:IamJakuhoRaikoben/Chapter 492: Elder Sister and Younger Sister, Review./@comment-25305529-20160704202202/@comment-7418318-20160704224140

Scenario:

Irene dominates Mira and is about to finish her off. Lisanna: "Mira I will save you!" Lisanna punches Irene. Irene stares at Lisanna disbelieving. Lisanna keeps punching and kicking Irene, but Irene just stands there staring at Lisanna. After a while Lisanna is exhausted and stops attacking, with Irene still staring disbelieving. Irene: "Did you seriously think you can harm me with such little power?" Lisanna: "Yes! I spent the entire last year training with Mira-nee and now I'm super strong!" Irene breaks out into histerical laughter. After a while she tries to catch her breath, but just can't stop laughing. Irene dies from lack of oxygen. She literally laughed herself to death.

That seems about the only reasonable way for Lisanna to save Mira. :P