According to Yuko's memories when I asked her before, she told me how she started remembering things weeks after our first meeting and how I seemed to be acting mature while she's like a kid who always wanted to be spoiled by me.
However, that might just be her perspective of what's happening to us. I could now clearly remember how childish I was when it came to her. The mature part of me that probably made its mark on her was when I was dealing with the other kids to leave us alone.
At that time, Yuko alone was enough for me and she's the same.
About the things she began to remember as days passed by, they were the dreams that she often narrated to me whenever we're together.
And confirming what she remembered, the Convergence of our Destinies happened ever since that first meeting. The days leading to the full awakening of our memories were just us spending time together.