Attack on Titan isn't known for its plethora of on-screen romances. Hajime Isayama's brutal action saga about humanity's battle against the monstrous Titans is largely devoid of emotions beyond anger, guilt, or sadness, and, while romance is not completely absent, it is not a prominent feature of the story.
With most of humanity living under the constant threat of being killed in war or eaten by a Titan, it comes as no surprise that many of the romances in the series are either short-lived or unreciprocated. While some romances further the story such as Dina's and Grisha's doomed union or add complexity to relationships such as Eren's and Mikasa's complicated love affair, others feel forced or just downright weird.
Carla And Grisha
At the start of the series, the relationship between Eren's parents seems like a normal romance. At first glance, Eren's parents appear loving and happy, and, while his father's past is steeped in mystery, there are no oddities concerning their overall relationship.
However, once's Grisha's backstory is revealed, his whole relationship with Carla is cast into doubt. His marriage to Dina in Marley makes sense given their shared belief in the cause of the Eldian restorationists, but Grisha's subsequent marriage to Carla feels more like a cover than an actual romance given his mission to recover the Founding Titan from the Reiss family. While it's revealed that Grisha did love Carla and Eren, his motivations for starting a new family on Paradis Island feel muddled.
Historia And The Farmer
Little is known about how Historia got pregnant. Her mysterious partner is referred to only as The Farmer, and his identity is never revealed. While Historia's motivations for getting pregnant are well-founded, what's less clear is why she didn't reach out to one of her trusted friends in the Scouts.
Given how powerful Eren and Armin have become, it's fairly certain that the two of them could have come up with arrangements to protect her and come up with plans to prevent her from having to inherit the Founding Titan from Eren. While the circumstances are understandable, they could have likely been avoided altogether with a concerted effort by Historia's friends.
Historia And Reiner
Much like Historia's and Eren's relationship, Historia's and Reiner's relationship never had any real hope of ever getting off the ground. While both are attractive blondes with serious dispositions, the similarities between the two end there.
Though Reiner expressed interest in Historia multiple times, as an enemy of Paradis Island, he never had any real chance with Historia, and Historia never expressed any interest in him. Additionally, Reiner's interest in Historia appears purely surface level based on her good looks, and the two of them never share any significant time together exploring each other's feelings.
Historia And Eren
Historia's and Eren's relationship goes through many stages over the course of the series from comrades to potential enemies to confidant and protector. What never felt realistic, however, was their potential for romantic feelings for each other despite Mikasa's brief feelings of jealousy after Eren and Historia share a brief conversation together.
Eren acts more like Historia's guardian or big brother than a lover, and there are simply no sparks between the two. Any coupling between Historia and Eren would pale in comparison with Historia and Ymir or Eren and Mikasa and feel more like a union of convenience than a true romance.
Annie And Bertholdt
Annie and Bertholdt were both a part of Marley's elite Warrior Unit and therefore spent a considerable amount of time together growing up in Marley and undercover on Paradis Island. Despite the fact that Bertholdt admits to having feelings for Annie, this pairing just doesn't make sense on any level.
Annie is serious, taciturn, and focused solely on accomplishing her mission, while Bertholdt is quiet, reserved, and sensitive. No matter how you look at it, their personalities simply don't align. There is no chemistry between the two characters, and the few scenes they share are devoid of romantic undertones.
Hange And Levi
A romantic relationship between Hange and Levi makes sense on a number of levels. They are both decorated officers in the Scouts, and their personalities balance each other out. However, there is no world in which the two of them become an actual couple.
Hange is more in love with her research and inventions than with other people, and Levi is only interested in serving as a weapon in the fight for the survival of Paradis Island. Both of them are wedded to their work and have little time for anything else, especially romance, so any relationship involving the two of them would be doomed before it started.
Eren And Levi
Eren and Levi is another relationship that could have worked under the right circumstances. Eren and Levi both have serious dispositions, are dedicated to protecting Paradis Island, and are deadly warriors who will stop at nothing to achieve their goals.
That said, neither Eren nor Levi have the emotional intelligence required to deal with each other's grim moods and tempers. They would likely end up at each other's throats before a serious relationship could develop, and neither has a romantic bone in their body necessary to heal the other's bruised ego. Eren and Levi are warriors through and through, and there is simply nothing left after that for a romance to blossom.
Armin And Mikasa
This pairing just feels wrong given Eren's and Mikasa's well-documented history and her obvious feelings for Eren. While Armin is highly emotionally intelligent and has grown to be more confident and assertive, Mikasa and Armin are simply not meant to be together.
Armin needs to be with someone sweet and gentle like him, and neither of those words could be used to define Mikasa. On the other hand, Mikasa needs someone who is passionate and serious, someone who balances her cool and calm disposition. Armin would likely just try to end up pleasing Mikasa, which would spell disaster, as she is forced into a position where she feels responsible for Armin's happiness.
Jean And Mikasa
The first time Jean met Mikasa during Scouts training, it was obvious that he was attracted to her, but Mikasa paid Jean zero attention. That interaction serves as the foundation for all future potential romance between the two.
Mikasa simply does not have room in her heart for anyone aside from Eren, and Jean is not assertive or confident enough to genuinely pursue her. Mikasa and Jean have developed a mutual respect for each other and a close friendship over the years, but their relationship excludes the possibility of romance. Jean deserves someone who can reciprocate his feelings, and, when it comes down to it, Mikasa is not able of doing that.
Falco And Gabby
The newest young love candidates in the series are Falco and Gabby, and their relationship feels a lot like Eren's and Mikasa's, except in reverse, with Gabby fueled with a burning desire for revenge.
However, while Falco clearly has feelings for Gabby, Gabby does not appear to return Falco's feelings. She is so obsessed with getting her revenge against the Eldians of Paradis Island that she has little capacity for anything outside of her goals for revenge. Also, Falco is much too sensitive for Gabby, whose temperament is more wild and assertive, and any romance between the two would suffer as a result.