Mikasa notices Annie's words and her looking towards
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.
In the Junior High anime it is heavily implied that Annie has a crush on Eren and the two of them bond over their shared love for cheese burger steak.
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.
Defeated by Eren's Attack Titan and the Survey Corps' sublime teamwork, Annie encased herself in Titan hardening to avoid being questioned or tortured. Her crystallized body has been collecting dust in a basement ever since.
Armin Arlert
After the battle in Stohess, Annie crystalizes herself. Armin would constantly visit her, after emerging from her crystal she and Armin form an alliance. On the boat to Odiha, the two then confess their feelings from one another. In the time-skip it's implied that they're together.
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.
AruAni is the het ship between Armin Arlert and Annie Leonhart from the Attack on Titan fandom.
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.
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.
Love Confession — Eren confesses to Armin that he always loved Mikasa, and can't bare seeing her love another man. Alternate Universe — Eren sends Mikasa a vision where Mikasa truly were to confess her feelings to Eren, the two then run away to live together as a couple for the remaining of Eren's final years.
But that's the key point causing fans to wonder about Annie. Eren almost ate The Warhammer Titan's host while she was encased in a hardened shell. This seems to indicate that Eren believed his Titan body could still “kill” the Titan even in its encased shell if he ate it.
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.
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.
Not much is really known about Annie after her defeat, she has cried twice throughout the series (the second time is a spoiler) but from what evidence we can gather is that she saw that her mission was a failure and was saddened by it.
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.
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.
In S1 there were hints that she did like him: Her letting him live is what got her caught. She wanted to be "a good person" for him and helped him try and smuggle them out.
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.
Jean immediately develops a crush on Mikasa upon seeing her for the first time, causing him to blush and stutter. He tells her that she has beautiful hair, to which she replied with “thank you”. When Mikasa leaves, Jean follows her, wanting to say something more, but stops at his track when he sees her with Eren.
Unfortunately, Annie and Armin do not get married in Attack on Titan. The romance between the two characters develops quite late in the story, and the author only briefly touches upon it.
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.
While there's no way they are siblings— they have different parents, after all— there's evidence that the two of them are distant cousins, especially when considering the power they share with Kenny.
Leonhart (レオンハート Reonhāto?) is the father and trainer of Annie Leonhart. He relentlessly trained Annie to fight, using mostly kicks and the attacker's weight against them. Memories of his pleas for forgiveness later create an opening for Annie to crystallize herself before Eren Jaeger has the chance to capture her.