Kara was born on the Planet Krypton and is the daughter of Alura and Zor-El. She had a happy childhood and admired and deeply loved her parents. Kara and her family were known to go visit numerous planets for family hoildays. However, Kara's life changed forever when the Planet Krypton was destroyed, her parents managed to save Kara and her baby cousin Kal-El, allowing them to escape the Planet's destruction and go to Planet Earth. Kara's parents instruct Kara to protect and raise Kal-El. However, when Kara escaped the Planet's destruction, the pod she was in went off course and for years she was stuck in the Phantom Zone. Later, the pod containing Kara managed to break free and she eventually made her way towards Earth only to learn Kal-El grew up and has already become Superman.
Kara is sent to live with the Danvers family, close allies to Superman and they become her adoptive family consisting of Jeremiah, Eliza and Alex. Kara was forced to keep her powers a secret from the public and tried to grow up and have a normal life for herself. While Kara struggled to hide her powers and live on Earth, she came to adjust with the support of her adoptive family and developed a close relationship with Alex. However, Kara still deeply misses her parents, but still loves the Danvers for all they've done for her.
Mon-El is Kara's new main love interest in the second season of Supergirl. Kara and Mon-El first met on the first season finale of Supergirl when Mon-El's escape pod from the planet Daxam arrived and crashed landed on Earth. However, Mon-El was in a comatose state and Kara originally believed he was one of the last survivors of Krypton as he held the same powers as herself and Superman. Later, Mon-El had awakened, but shock by his surroundings and newfound powers, he quickly escaped from the DEO and later tried to get into contact with his home planet to return home. While tracking him down, Kara eventually discovered the truth that Mon-El is actually a survivor from the planet Daxam and instantly believed him to be a bad and untrusting person as both the planets Krypton and Daxam never got along with each other. Kara believed him to be the alien assassin who was attempting to kill the president upon learning of his true origins. Mon-El tried to explain himself, but upon seeing that Kara has already judged him, Mon-El refuses to further speak with her.
Eventually, once capturing the true culprit, Kara freed Mon-El and apologizes for misjudging him and reveals the tragic truth that Daxam was destroyed alongside Krypton. Throughout the season, Kara helps Mon-El to adjust to life on Earth and how to properly control his powers and begin to grow close. However, they still face issues as Mon-El has different views and opinions on what he wants for his life on Earth and Kara constantly judges him whenever he appears to be selfish or spoiled. The bad history between their two planets also doesn't improve their relationship as occasionally it has caused serious issues. However, they both learn to overcome their differences and gradually they start to become friends. Mon-El and Kara also help influence the other as Mon-El helps Kara to relax more and Kara encourages Mon-El to become a hero and use his powers to help others. Kara and Mon-El grew even more closer together when they were both captured by Cadmus.
Eventually shortly after being rescued, Mon-El began to developed romantic feelings for Kara. Everyone soon became aware as his feelings for Kara were obvious, but Kara remained completely oblivious until her adoptive mother Eliza revealed her awareness of his growing romantic feelings. When she learns of this, Kara tries to speak with Mon-El regarding his feelings although he denies her claims, Mon-El collapses from an alien virus before they further talk of their situation.
Unknown to Kara, her feelings for Mon-El began to grow as she became extremely worried about him when he was dying from a fatal virus created by her father that can kill any alien except Kryptonians. Kara felt an extreme guilt for what was happening to Mon-El and their feelings ultimately escalated when Mon-El kissed Kara. Kara was shocked and surprised and wished to speak with Mon-El about the kiss only to discover he apparently doesn't remember. However, unknown to Kara, Mon-El does remember, but is afraid and nervous to speak with Kara in regards to how he really feels about her and her own feelings in return.
Later upon accompanying Kara to an alien slave world to save several humans who were kidnapped, Mon-El finally decided to become a hero, thrilling Kara. They began training and their first mission was facing off against Livewire who somehow managed to escape from Prison. However while Kara told Mon-El to keep the citizens safe, he jumped to help protect Kara when she came close to being severely hurt, leading to one civilian becoming hurt and finally discovering James is Guardian. Kara became mad at Mon-El and begins to believe he only wants to be a hero to work alongside her due to his feelings and once again confronts him of his real feelings towards her. Once Livewire is gone and the real criminals are defeated, Mon-El meets with Kara and reveals he does remember the kiss between and finally confesses his true feelings for her. However, Mon-El understands and accepts Kara doesn't feel the same, but still wishes for them to continue to work together.
While Kara originally did not feel the same way towards Mon-El, Kara comes to realize she feels the same way about him after his confession, but attempts to distract herself. When Alex realizes Kara's struggle and approaches the subject, Kara finally admits that despite her denial, she does return Mon-El's feelings. However, Kara also reveals she is afraid to start a romantic relationship as she has somehow almost always gotten hurt. Alex assures and encourages Kara to give Mon-El a chance to have a relationship together. Taking Alex's advise, Kara attempts to confess her feelings, only to discover and become jealous when she learns Mon-El and Eve have started dating.
While it appeared that Mon-El had moved on from Kara, she learned from Eve that they are not romantically together as Mon-El still harbours strong feelings for Kara. When Kara confronts Mon-El about lying of the true nature of the relationship between him and Eve, he realizes she is actually jealous and tries to confront Kara regarding her real feelings. However, Kara refuses to confess the truth and instead avoids the topic. Later, Kara invites Mon-El to her apartment and begins to admit that despite their differences, Kara begins to confess her true feelings and admits that she was unsure if she could still be Supergirl and have a romantic relationship. However, since meeting Mon-El, she begins to think it may work, espically since he has managed to prove himself time and again and has become a better person than what she originally thought. Kara and Mon-El are about to kiss until they are interrupted by the arrival of Mr. Mxyzptlk, an extra dimensional being who suddenly arrives at her home, declares his love and desire to marry her.
Although Kara refuses Mr. Mxyzptlk romantic advances and refuses to marry him, he still continues to pursue her and even attempts to make threat to force Kara to marry him. Mon-El becomes extremely jealous and eventually everything worsens as it causes serious arguments between Kara and Mon-El. Mon-El attempts to stop Mr. Mxyzptlk himself before he can cause anymore harm, but is nearly killed himself until Kara arrives and agrees to marry Mr. Mxyzptlk. Later, Mon-El arrives at Kara's apartment and tries to apologize for the night's previous events and to convince her not to go through with the marriage. Kara refuses claiming marrying Mr. Mxyzptlk is the only way to stop him and that using his powers might help fight against evil. Kara further admits that it was wrong to think that they could begin a romantic relationship. Heartbroken, Mon-El leaves Kara's apartment.
Later at the Fortress of Solitude, Kara meets with Mr. Mxyzptlk, once again expressing her refusal to marry him and after a brief fight, she manages to trick him and send him back to his dimension. Mon-El visits Kara, congratulating her on defeating Mr. Mxyzptlk and again apologizes for how he acted. Mon-El once again expresses his feelings, admitting Kara is his Kryptonite and how he has never felt so strongly about any woman before until now.
Mon-El cares about Kara so much he is willing to leave her alone and attempts to leave until Kara stops him. Kara reveals she didn't mean anything she said before, revealing, she only said those things to protect him while she faced Mr. Mxyzptlk herself and wanted it to sound believable as he could possibly over hear them with his powers. Kara assures Mon-El and they finally begin a romantic relationship and share a passionate first kiss, marking the offical start of their romance. While they had a somewhat rocky upstart to the beginning of their romance, they quickly form a strong and loving relationship. They continue to make each other better as Mon-El understands Kara can take care of herself, but remains protective of her and becomes a better listener in regards to her well being and wants. However, while their love for each other remains strong, they soon encounter a serious problem that threatens their entire relationship.
Kara discovers that despite the destruction of Daxam, Mon-El's race survived including his parents and learns the shocking truth that he is actually the Prince of Daxam. Kara begins extremely hurt by his lies and is more upset when she learns the true story about how he escaped the destruction of his planet, involving the death of a Kryptonian. While Kara's family and friends know Kara has the right to be upset with Mon-El, they also encourage and advise Kara to speak with Mon-El about the reasons why he kept the truth from her and to try and see from his point of view. Mon-El constantly apologizes to Kara, revealing how he is happy she has made into a better person and declares his love for her. However, believing she doesn't know Mon-El anymore and refusing to forgive him, Kara breaks off their relationship much to her own heartbreak.
However, shortly after their breakup, Kara and Barry Allen both encounter an extra dimensional being known as the Music Meister, placing both of them in a comatose state. He places them in a musical illusion world where they have to play out the storyline to escape and free themselves. They discover their respective love interests, Mon-El and Iris are romantically together in the musical world and must keep their love a secret from their families who at war with each other. Kara and Barry must help them to get their families to accept their love and in the process, both discover they were facing the same problems within each of their own relationships. Kara came to realize her mistake, realizing she wasn't listening or trying to understand the reasons why Mon-El chose to keep his true identity a secret. Kara also acknowledged that one of the main reasons why he didn't confess the truth was because he was afraid of how she would react.
Later, both Barry and Kara were severely injured and came close to death until both Iris and Mon-El entered the musical world to free them. Both couples reconciled, declare their love and share a kiss, awakening Kara and Barry. Upon regaining consciousness, the Music Meister reveals that despite his methods he was actually helping Barry and Kara. He gave them both a lesson in love to help reconcile with Iris and Mon-El and reminding them that although they are superheroes, they also need to be save as well. Kara and Mon-El ultimately reconciled and got back together.
Later, Mon-El is forced off of Earth as a result of a lead bomb created by Lena Luther in order to get rid of the invading daxamites and dominators. Mon-El disappears for several episodes before he is discovered at the bottom of a lake in a space pod. While on Kara's Earth it has been approximately 7mths since Mon-El left, for him, who has been living his life several centuries in the future, it has been 7yrs. He is revealed to have since married a woman from the future Ember (Emma).
James Olsen was originally Kara's main love interest in the first season of the series. In the beginning of the second season although Kara and James attempt to start a relationship, Kara decides it's better they remain friends as although she held strong feelings in the beginning, she no longer desires anything more between them.
Winn is Kara's best friend and former co-worker at CatCo Worldwide Media. Ever since Kara first arrived at CatCo, Winn instantly developed strong romantic feelings for her, but Kara remained unaware of them and only saw Winn as her best friend. Since she began working at CatCo, they developed a strong friendship, but Kara remained completely unaware of Winn's feelings as they grew more stronger over the years.
Adam Grant is the oldest son of Kara's boss, Cat Grant and a brief love interest in the first season.
- In the first season, Kara's original love interest was James Olsen.