Kami nomi zo Shiru Sekai (The World God Only Knows) - I love the anime, still gotta watch the second season. I have read the manga and is sad that the pairing I was shipping didn't get together in the end.
Pokémon evolving with their trainers. I had my own idea similar to this for Halloween someday, with a cosplay-like thing based off one of my favorite Pokémon. I had Dratini, Riolu, Dragonite, Lugia or Torchic in mind.