WARNING: The following contains spoilers for Attack on Titan Season 4, Episode 22 "Thaw," now streaming on Crunchyroll, Funimation and Hulu.
With an army of elite soldiers combating towering humanoid monsters, Attack on Titan doesn't lack characters whom viewers deem as badass. The anime features a variety of soldiers ranging from the brainy Hange Zoe to the stoic Titan-killer Levi Ackerman. Mingling among them is another fan favorite, Mikasa Ackerman.
Mikasa has been following protagonist Eren Yeager ever since she lost her parents and the boy rescued her from kidnappers, which is also why she enlisted in the military. Even though her only desire is to protect Eren at all times, she turns out to be a talented soldier who's capable of that and so much more. Mikasa's superb Titan-killing skills allowed her not only to save Eren but also many others -- and in Season 4 Episode 22, she proves her might once again to a longtime admirer.
With Eren initiating his grand plan to exterminate all of humanity except for the Eldians, the Titans ran amok and started to attack everybody in sight. The military was quick to react, swiftly equipping themselves to fight their former comrades. However, the new batch of Titans proved too great a threat for them to escape unscathed. With the members of the 104th Training Corps taking the lead to eliminate the Titans, Mikasa once again showcased her might by singlehandedly and fluidly eliminating a number of the man-eating behemoths in succession. By doing so, she managed to save Louise -- the same girl she saved years ago in Attack on Titan -- for a second time.
During the "Battle of Trost District" arc, a good amount of citizens were being barred from entering the city as a selfish merchant, Dimo Reeves, prioritized his cart of mercantile over the people. The young Louise was one of those people, and was also the one who spotted an Abnormal Titan charging toward them. Just before the Titan did any damage, Mikasa swooped in and slew it, earning the young girl's admiration.
Louise's admiration for the female soldier prompted her to enlist in the military and join the Survey Corps as well, and her idolatry toward Mikasa helped shape her own morals. She firmly believed that one must fight back when threatened, just as Mikasa did when Louise first met her. This resolution led her to sympathize with Eren's cause and join the cult-like Jaegerists. Louise was one of the individuals who leaked news about Eren's imprisonment and was also arrested by Hange. Even then, she was disappointed at not being held in the same cell as Mikasa.
Louise also attempted to talk Mikasa into joining their cause, but the latter cut her off in disinterest. Nevertheless, Louise saluted her hero as she walked away. Mikasa's recent rescue further strengthened those feelings, and Attack on Titan highlighted it perfectly by capturing Louise's awe as Mikasa fluidly eliminated one Titan after another.
Mikasa is undeniably one of the most endeared and beloved characters in Attack of Titan, though it is arguable whether or not she's the best girl in the entire series. However, she is and will always be the best girl and mightiest soldier in Louise's eyes. Mikasa saving her for a second time cements her position in her fellow soldier's heart.
