Mirajane is the 7th strongest wizard in Fairy Tail. Don't let the her pretty face and kind heart fool you because when it comes to defending her brother (Elfman) and sister (Lisanna) and of course Fairy tail there is no stopping the true demon inside Mirajane.
When Mirajane was younger she tried to save a church from a demon by doing so the demons powers transferred to her making her arm look demoninc causing the townsmen to kick her and her brothers out of town. When she meets Makarov he tells Mira that it is a type of takeover magic. Thanks to that demon and her family Mira has become a very strong female wizard. Having three main demon transformations that's are as powerful as they are deadly. Her first demon takeover is called Satan soul. After Satan soul she can become an even more powerful Satan soul called Halphas. Her strongest Satan Souls is Sitri. I don't know about you but if she can turn half demon and become and then turn into an even stronger demon I wouldn't want to even mess with her in the first place.
In the Tartaros Arc. Mira comes face to face with one of the Nine Demon Gates of Tartaros names Seilah. Thanks to Mira the lab in the Tartaros guild that helps bring back a demon when killed is destroyed thanks to her incredible takeover magic. Mira being Part demon herself makes it hard for Seilah to use her curse magic on her. Seilah also being a demon makes it hard for Mira to use her takeover magic on her as well. Both being unable to use their signature moves makes this battle a battle of physical strength. Seilah before meeting Mira used her curse magic to take control over Elfman making him to choke his sister lisanna when Mira found out she went into her mode and fought with all her might and tried once again to use her takeover magic on Seilah and takes control over one of her powers which is to take control over someone and Mira tells Elfman to come to her side and helps defeat Seilah once and for all. I love Mira because she teaches us that with family we can conquer anything together and I can't wait to see get stronger in the future as well.