Byleth and Edelgard
Byleth does not add a lot of impact on the supports since they are silent with a few choices of what to say, but there is some merit to this one with Edelgard. Both genders share the same conversation, including S rank. This support conversation does carry a lot of weight to the story of the Black Eagles route, which in turn, lands a spot on this list.
We learn a lot about Edelgard’s backstory and the tragedy of her family. All of her siblings were killed off, and she was the only one to survive. She, along with them, went through experimentations of having crests implanted on them, and we find out that she bears the same crest as Byleth, although artificially. Despite what she went through, Edelgard still carries out her duty to become the next emperor.
The B support can only be activated when the player goes with Edelgard and does not kill her in the Black Eagles route. It acts somewhat like a filler arc since Edelgard wants to do nothing but eat countless sweets (relatable to a T). Because of Byleth choosing to stay by the emperor’s side, she can not only rule with confidence but also be herself.
The A support has Edelgard talking about how Hubert is making her do her usual duties, and the player can say that it is what Hubert would or would not do. Regardless, Edelgard thanks Byleth for helping her in battle. She then admits her jealousy towards Byleth’s talent in strategy, but then proceeds to ask them to call her El, as her parents and sisters did so. Then she ends the conversation by saying that Byleth is like family to her, and it is a sweet way to end the support unless the player wants to S rank Edelgard.
The conversation between the two help make the Black Eagles route a trip to encounter, at least in my playthrough. Knowing of Edelgard’s tragic backstory while also overcoming it to help the people of Fódlan is remarkable, even if she walks on the path of blood.