I think the main reason why he fell for her was HER VOICE. He was attracted to it even before he saw her.
Her voice gave him the inner peace of mind that he was looking for. Calmed the storm that is always brewing inside him. He in fact admitted to it in their very first meeting that he got sukoon the very first meeting.
There also some little actions /qualities whatever you call like helping others like during the mask festival she gave her Loot to the needy.
There was also a scene between the 3 where Arohi says she wants to be the best like Abhimanyu. That very moment Aksara says I just like the way I am. I think that left a very deep impression.
Abhimanyu comes from a household where everybody is in a race to be the best of best. Those who do not participate in this race are considered to be useless or non existent therefore seeing someone standing for what they are really touched his heart ..
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