Balder admires Amora's assertiveness and refusal to be limited, as these are qualities he finds lacking in himself. His attraction to her began in lessons, when the boy would often be distracted from some of his schoolwork by the disciplinary problems that would arise from Amora's contrary nature, though he at times found the quipped comments she would make on the subject matter of the lessons echoed his own sentiments (ones he could never bring himself to voice) and her truancy on particular days left him somewhat envious, particularly when it coincided with tests on figures, a subject for which he has never displayed talent. His attentions, however, remained in the background, as his overwhelming shyness and lack of self-worth and confidence left him admiring from afar at her gumption and expressiveness. It was the beginning of his romantic predilections to 'bad girls.'
(On an additional headcanon-y note, I had before that Amora and her sister Lorelei, though aware of their parentage, are fosterlings like Balder, and this shared experience of displacement and lack of a sense of belonging was a point they shared. However, Amora's reaction to different moves between houses resulted in her acting out and misbehaving, something Balder could not comprehend doing, as he felt strongly--perhaps pathologically so--that doing everything right and according to the expectations of his foster parents would ensure his stay with a family was lengthened, hopefully to permanency and adoption. It was on this point of contention--Amora's disregard for obeying established rules within households and seeming lack of care for which family would keep her--that eventually caused Balder's childhood crush to fizzle. Whether or not your Amora would like to fit into a scenario like that is up to you.)