Magic Knight Rayearth was when I discovered that I was into girls, so I have a soft spot in my heart for it despite it probably being CLAMP's most heterosexual offering. Umi was my first female crush I actually recognized as a crush.

As for fannishly, Vocaloid was my fist 'wow, there's a lot of femslash here, and I really like it' fandom. I had a great time there. Tragically the biggest f/f ship got in the way of my f/f otp.