With Yaz and Thirteen having recently begun to talk about their feelings for one another in Doctor Who's "Legend of the Sea Devils," many fans are hoping that this potential romance will not end in tragedy (like the relationship the Time Lord's predecessor's had).
The last great romance that had been just as iconic as theirs had been between the Twelfth Doctor and Clara Oswald, and despite their incredible chemistry and deep relationship, they could never find the right time or get on the same page. Nevertheless, whether it is because of their very tumultuous beginning in "Deep Breath" to their bittersweet goodbye in "Hell Bent," fans did thoroughly enjoy watching this TARDIS team in action and rewatching their episodes.
Banter
The Twelfth Doctor and Clara Oswald always had a way with words and often would affectionately bicker with each other like an old married couple.
This starts as early as their very first episode "Deep Breath" and continues throughout their run. The playful back and forth they have is interesting because it emphasizes that they are on an equal level with each other. Rather than the Doctor just ordering Clara around, Clara often is the one bossing him around just as much as him.
Acceptance
The Twelfth Doctor and Clara both accept each other when they see the other in older forms. Even though Clara struggled at first with her Doctor's new older appearance, she proved that she wasn't shallow and fully came to love and accept him in his new form.
At the end of "Deep Breath," she hugged him after he asked her to "Just see me." The same applies to the Twelfth Doctor when he sees Clara as an older woman in "Last Christmas," and he doesn't even notice that she had changed, instead visualizing her as the same person he had always known and loved.
Hugging
Despite the Twelfth Doctor claiming to hate hugs he always accepted hugs from Clara. Throughout their time together Clara helped the Twelfth Doctor become more physically affectionate. Their hugs became progressively less awkward as their relationship deepened from Series 8 to Series 9.
In Series 8, their hugs were stiffer and The Doctor seemed resistant. However, in Series 9, he is far more comfortable and relaxed - even picking Clara up in a spinning hug in "The Girl Who Died." It was beautiful to see how far their relationship had progressed over the course of the many years.
Caring For Each Other's Happiness Above Their Own
The Twelfth Doctor and Clara Oswald always prioritize each other's happiness over their own. In "Death in Heaven," they each lied to each other so that the other could have what they thought would make them happy, rather than stay with each other. In "Hell Bent," the Twelfth Doctor brought back Clara from the dead and intended to wipe her memory so that she could live a happy, normal life. Clara eventually reversed the mind wipe so the Doctor didn't have the burden of grief over her anymore.
This shows how unselfish the Twelfth Doctor and Clara can be for each other. They would deprive themselves of being with one another if they thought it meant each other could be happy. Viewers often see this with the Doctor doing a one-way sacrifice for their companion, but it was rare to see a companion do the same for them too.
The Twelfth Doctor Wrote a Song for Clara
Ever since Clara's introduction in Series 7B, she has been accompanied by "Clara's Theme," (an iconic Doctor Who score), which is later revealed in "Hell Bent" to be a song the Twelfth Doctor wrote about what Clara said to him in the Cloisters that he can't .
No other Doctor has ever written a song inspired by their companion before. Also, due to the heavily implied context that what Clara said in the Cloisters was a love confession, that makes the song the Twelfth Doctor wrote about Clara a love song. This is an incredibly deep bond, for the Twelfth Doctor to write a song about Clara that is used as her theme, even before he is introduced as the Doctor.
They Changed Each Other For The Better
Throughout the best episodes of series 8 and series 9, the Twelfth Doctor and Clara have changed each other for the better, often taking on attributes of each other in the process.
The Twelfth Doctor became more sociable, softer, kinder, and more expressive under Clara's influence. Clara became much more adventurous and Doctor-like under the Twelfth Doctor's influence. It's not often that Doctors and companions change each other this much, with him becoming more human and her becoming much more like the Doctor.
The Twelfth Doctor Forgives Clara, Even When She Betrays Him
In "Dark Water," Clara betrays the Twelfth Doctor after Danny is killed, demanding that he save Danny or else she will drop his TARDIS keys down a volcano. Even though this betrayal isn't real and the Doctor drugged her instead, he forgives her and says this: "Do you think I care for you so little that betraying me would make a difference?"
The fact that the Twelfth Doctor forgave Clara even after she betrayed his trust shows just how deep their bond and his love for her is. He could have said no to Clara's request, or even kicked her out of the TARDIS. She betrayed him (or at least attempted to), but The Twelfth Doctor still forgave her and agreed to rescue Danny because he just wanted her to be happy. It's just too bad that it still ended in a tragic manner for Clara and Danny.
Clara Implied The Twelfth Doctor Was The Only Other Man Besides Danny She Would Marry
In "Last Christmas," the Twelfth Doctor is reunited with an elderly Clara, and asks her if anyone lived up to Danny. Clara responds that there was one other man, but that he would have never worked out because he was impossible.
This is heavily implied to be the Twelfth Doctor - especially since when Clara is a young woman again, she kisses him on the cheek, which was outlined by the shape of a heart in the background. Other companions have loved the Doctor, but no others have been implied to hold out for them when they are elderly.
The Twelfth Doctor Spent 4.5 Billion Years in His Confession Dial to Save Clara
After Clara died, the Twelfth Doctor spent 4.5 billion years in his confession dial being tortured so he could bring Clara back from the dead.
No other Doctor has ever gone to such extreme lengths to save their companion. The love and deep bond they have for each other made the Twelfth Doctor experience billions of years of misery that he could have left at any time, and risk time itself to bring Clara back.
The Twelfth Doctor and Clara Became The Hybrid
Throughout Series 9, there was a prophecy hinted at the real reason the Doctor ran away from Gallifrey. A hybrid of two warrior races would stand in the ruins of Gallifrey and destroy the web of time, and break a billion hearts to heal their own.
The hybrid is revealed by Me/Ashildr to be not two warrior races, but the relationship between the Twelfth Doctor and Clara. This is an incredible feat that the hybrid isn't some terrifying creature or being, but a bond and love between a Doctor and human companion so powerful it nearly unravels time itself. This prophecy that terrified the Time Lords so much existed just because the Doctor and Clara loved each other that much.