Let's talk about the relationship between Levi Ackerman and Hange Zoe
Everything mentioned below is canon.
As we can see, they are very close and know each other very well, even surpassing the phase of best friends.
And we can also see them always next to rach other, Whether during or outside of work, in good or bad times.
It is said by isayama that levi once tried to kill himself but was stopped by hange and erwin.
Also, when levi arrived at the Survey Corps with his friends, Hange was the first one to be kind and spontaneous with them, to the point of leaving Levi surprised by her upbeat and energetic attitude (choice with no regrets manga)
And let's not forget the fact that levi often knocks hange unconscious, so he can bathe and clean her (hange's interview), so he saw her many times naked since he is the one bathing her.
Now let's see levi's reactions whenever he sees hange around another guy (except Erwin and Moblit)
When she was trying to get information out of pastor Nick :
And when they captured Nicholas, she tried to negotiate with the Marley soldiers :
We can clearly see that levi is somehow jealous and angry at the way hange behaves with them, even going so far as to touch them in front of him.
Levi and Hange are very important to each other, they are always worried and scared when one of them is in danger :
Hange even protected him with her body, risked her life and escaped with him from Zeke, Floch and the yeagerist.
Levi is known to be a cold, serious and intimidant person, no one dares to respond or argue with him, But with hange, it's different, she gives him back his shit jokes with more shit jokes, she changes his plans for Eren without asking him, and he just lets her get away with it without saying anything, He knows it's her just by the way she knocks the door, they always drink tea together in their break, she's the only one that he allows to touch him, once, he grabbed her by her hair and bring her closer to him (her hair being known as canonically greasy, he does'nt care even if he is a freak clean), She knew that Levi lived with Kenny when he was a kid, that means he talks with her about personal things .....
They are the exact opposite but complete each other, that's what attracts them
Levi being a cold, distant person, having no energy obsessed by cleanliness
In the other side there is Hange the Energetic, friendly and curious one.
Even in their injuries, Hange loses her left eye, Levi losing his right one, Together united forming a pair of eyes and wings, wings of freedom, like a real Jian Bird
After saving him from Zeke and healing him, once he woke up, they opened their hearts to each other and expressed their frustrations, Hange even wished to live just with Levi, alone in the forest, but they couldn't let the rest of their comrades die, because he was humanity's strongest, and she was the commander, they carried heavy responsibilities on their shoulders.
However, that didn't stop them from giving each other warm, heartwarming looks.