Ahh, while the MC may not recognize Ai, in her heart she is already in love with her still. That is why the MC was crushing on her at "first" meeting, which wouldn't happen to the MC with random strangers. I chose this ending to represent the idea that you can always fall in love again if your love was true. There is also a number of real life stories where people with permanent memory loss still manages to fall in love with their partner again. Also, this ending would allow Ai and MC to have more equal footing when they restart their relationship.