JeanKasa

JeanKasa is the het ship between Jean Kirstein and Mikasa Ackerman from the Attack on Titan fandom.

Canon
Jean immediately developed a crush on Mikasa upon seeing her for the first time, causing him to blush and stutter. He found her long black hair in particular to be very beautiful.

During the Battle of Trost part 3, Jean and the other cadets were stuck on the roof with little to no gas left. He remarked that it had been a dull life and how he had never got to tell her how he felt.

Jean also appears to be jealous of Eren whenever he is with Mikasa.

When Mikasa stayed with Eren while he was hurt and in bed, Jean could be seen with a depressed face as he walked out the door, leaving them alone.

In the OVA for Jean, he was seen drawing a picture of a pretty girl under his blanket in his room whilst his mother yelled at him from downstairs. He seemed to be rushing it and the picture looked fairly like Mikasa. The fandom had taken it to call the drawing “Jeans Dream Girl” implying that Mikasa is the girl from the drawing, even though the two hadn’t met yet.

After Mikasa's ribs were crushed by a titan, Jean was infuriated and stabbed the titan in the eye, freeing Mikasa and saving her life.

When Jean was disarmed and about to be shot, Mikasa rushed to try and save him. However, it was Armin who ended up saving him.

Mikasa was shown treating Jean's wounds during the mission to retake Wall Maria.

Fanon
Considering recent developments in the manga showing everyone, including Mikasa, to have lost faith in Eren, it is possible she will not love Eren forever and fall for someone else instead. This could be Jean given the fact that they have spent four years in close proximity with each other.

Fandom
AO3