It would be foolish for anyone to think they could find a place in Mikasa's heart. Especially foolish if they sought to unseat Eren Jaeger, the man she focused practically her entire life upon. Even Captain Levi had remarked on it once-"I have no idea why you're so devoted to this idiot, but if that's the case, make sure you defend him with all you've got."
Eren saved her life as a child, and she his. He was there when she awakened into her Ackerman abilities, there when she soared through the 104th squad to the top of the class. His family took her in as their own, and became her family. She loved them and Armin with all of her heart.
The ability to do what needed to be done. That was what little power she had. And she would use it, absolutely, to defend those she loved.
Still, regarding Eren, she found somewhat of a doubt seeded in the depths of her heart. She had no doubt that Eren cared about her-he would give his life for her, that much she knew to be true. She knew it in her bones. And though he would mourn her death more than a random member of their squad, she also knew that he would give his life for any of them, and it made her feel...replaceable. In truth, it made Mikasa wonder what she was to him.
At no point had he ever hinted to her that he viewed her as anything more than an extremely important member of his family. He'd never suggested that they become anything more than comrades, never spoke to her the way a man speaks to the woman he loves. She'd never seen a hint of something like romantic love in his eyes. Devotion, but not passion.
It got to the point that Mikasa did not expect that she'd ever receive that level of affection from him-and she learned to adjust her expectations. Even this would be enough, the way things were now. Being able to protect him and live beside him would be enough.
So when someone like Jean came along, someone who was so utterly floored by her beauty and abilities, she was taken aback.
Just a glance at Jean was enough to know what he was thinking. You are beautiful. You are amazing. I want to be around you. He was overflowing with it.
A naturally standoffish person, Mikasa immediately rebuffed his advances. She didn't know him, and felt somewhat suspicious of his intentions at first.
And yet at night, before drifting off to sleep, it would wiggle into her head. The notion of someone explicitly pursuing her...She felt a flutter of excitement.
But no, that emotion was stupid and unwarranted. She pushed the thoughts away, focusing on the two people she loved the most. Armin and Eren were already a handful, and gave her plenty to worry about. She didn't have time for such girlish hopes.