Eren: Eren's father usually went to your house to do daily check-ups on what was your always sick family, and Eren had to come along. He found you in your room and talked to you the entire time to pass off his boredom, and after he left your house, you secretly wanted to get sick on purpose so he could come back.
Mikasa: You lived near an isolated forest in Wall Maria, and your curiosity just got the best of you and you decided to explore the forest. You found out that there is a family that lives in a cabin in the forest, and, after knocking on their door, you soon met a shy and lonely girl named Mikasa, along with her parents. You talked to her for a while and even took a walk with her, which was very refreshing.
Armin: Armin showed you a book, which is how you first met. The book was apparently written by people who have traveled outside of the walls and seen vast and vivid landscapes full of ice and heat. Armin said that he would go there to these places, and you wanted to follow him there, even if those places just seemed like a bit of one's imagination.
Levi: Before the Fall of Shiganshina, you saw the Survey Corps outside on their horses coming back from an expedition, and everyone was looking at one person; Levi Ackerman, humanity's strongest, and he looked at you for a split second while he was walking; a glimmer in his eyes. You couldn't believe it for the next few days, and you went crazy telling it to your friends.
Erwin: He first met you when you graduated the Trainee Corps, and he definitely wanted you to join him in the Survey Corps. He saw potential within you to make a great soldier; your physical skill, your smarts, and your humanity within you was something special to him. You ended up joining the SC and talked to him afterwards.
Hange: You don't know what words you exactly heard, but there seemed to be a sort of pained screaming a few meters behind you, and when you turned around, it was your superior, Hange, screaming over a captured and dead titan (not Sawney or Bean). You decided to comfort her, and you thought you did a good job at consoling her. Emphasis on thought.
Mike: Since you just joined the Survey Corps, you decided to explore around Headquarters to possibly make new friends and get familiar with the layout of the buildings. You stumbled across a pretty tall guy, and when you tried to say hello, he just sniffed you for a while. (You smell like vanilla to him)