So, her reasons for not killing Armin may be: Armin was harmless. His vertical maneuvering skills were poor, and even if he were to attack her titan form, she would easily squat him. She does not think of herself as a monster, or even that she is evil, so she has zero motivation for random killing.
Annie stop and look at armin's eyes and she armin. Annie didn't killed armin was the right thing to do. Armin was the first to figure out that annie was the female titan. Annie was wanting to capture eren, but that's not the point.
This is despite the fact that Annie acknowledges later being aware that leaving Armin alive would likely lead to him being able to use his wits to identify her as the Female Titan and thus potentially jeopardizing her mission. However, her growing feelings for him caused her to allow him to live.
This means that despite Armin and Annie's feelings for one another being hinted at enough times, in the manga, there is never a confirmation of these characters' romantic relationship.
Suddenly, Armin begins to yell that Jean must avenge "that suicidal blockhead," referring to Eren. He yells that she killed him in her rampage through the formation. Initially, Jean thinks that Armin has finally lost it until he sees that the Female Titan has stopped moving allowing him a chance to escape.
Annie showed a willingness to kill for the betterment of her goal, yet Armin, a major risk to her progression, was spared. It is most likely that Armin found Annie intriguing due to her history and actions, and that his inability to fully understand her motivations kept him interested.
Her doom stare is a mixture of disgust and rage at Armin's blasphemous deception.
Bertolt Hoover
Bertolt has been in love with Annie since they were children, and both were Warriors from Marley alongside Reiner. It's unknown if Annie knows about Bertolt's feeling towards her.
In the Attack on Titan Junior High series, it's heavily hinted that Annie has a crush on Eren, who's very oblivious towards it.
Plot twist, she actually like Armin this entire time. They have this small heart to heart where Annie was able to find solace in Armin because he visited her when she was crystalized. She asked him why he did that and Armin confesses that he secretly likes her.
Bertolt and Annie were both Warriors from Marley, and Bertolt developed romantic feelings for Annie. It is unknown whether Annie knows about this. The two, along with Marcel and Reiner, are sent to Paradis to retake the Founding Titan.
Annie is genuinely selfish, due to having been abandoned at birth and being used as a tool by everyone she has ever known, even by her adoptive father who wanted a better life for himself through her. She has no interest in protecting strangers due to being unattached to most of humanity to an absurdly high degree.
Now, while he never did express his feelings towards anyone, nor did he end up with anyone, there is someone that was, quite possibly, his principal romantic interest – Annie Leonhart. The two share a mutual respect for each other, expressing admiration for each other's hidden qualities.
4 Armin Arlet
A once feeble boy who was known for his intellect and had never recorded a single titan kill now has a conscience clouded with the death of countless people. After inheriting the Colossal Titan from Bertholdt, his explosive transformation at sea during the attack on Marley destroys a dozen naval ships.
Armin was the right choice because even though Erwin was a great leader, his entire life's goal was to prove his father's theory. He cared for the Survey Corps, but he was definitely willing to gamble all their lives for this.
Hoping he will lead her to the real king of the Walls, Annie decides to follow him. When Kenny discovers and confronts her about it, Annie attempts to deceive him by telling him that she is his long-lost daughter. Unsuccessful in fooling him, Annie attacks Kenny and flees into the sewers.
After all, Mikasa has been jealous of Annie before, and we see it during training. Mikasa is clearly aware of Annie's intentions and decides to intervine because everyone in the world knows Mikasa loves Eren and all that jazz.
The FBI has learned that Annie's parents are actually David and Margaret Bennett, who died some time ago; Annie truly is an orphan. Mr. and Mrs. "Mudge" show up to take Annie and the money, but are quickly exposed. They are arrested by the Secret Service, along with Miss Hannigan.
In particular, Bertholdt seemed to harbor some feelings for Annie, as observed by both Reiner and Armin.
While there are many characters that he respects, Erwin Smith is perhaps the only character that Captain Levi has truly loved, which puts Erwin at the very top of the list. Levi's loyalty and devotion to Erwin also indicate that the two were meant to be together.
No, Levi doesn't really have a love interest. Hajime Isayama (the creator) has said that Levi isn't the type of person to get into a relationship or have feelings for anybody.
When it comes to Attack on Titan's main trio, most fans have come to the conclusion that Armin and Mikasa are simply platonic best friends. These two always have each other's backs, but there's never been a scene or bit of dialogue to suggest that either of them is interested in anything beyond friendship.
With this in mind, Eren's laughter becomes something much more ominous. It becomes a sign of not only despair at losing Sasha but his resignation to the future. Sasha's death may have been the thing that drove Eren over the edge, forcing him to confront the absurdity of resisting his fate.
Armin leads Eren, Mikasa and Annie to a tunnel, but Annie refuses to enter. Armin finally reveals his suspicion that Annie is the Female Titan, noting that she used Marco's omni-directional mobility gear to kill Sawney and Beane and that the Female Titan did not kill him during the 57th Expedition.
Yelena and Zeke have a type of idol-fan relationship. She regards him as a god since she saw him for the first time after he saved her life during the Marley Mid-East War. She follows his commands without question, believing he is the one to save the world.