The characters are:
Racer X (Speed Racer), American Maid (The Tick), Kodachi (Ranma 1/2), Lady Jane (G.I. Joe)
The Brain (Animaniacs), Judy Jetson (The Jetsons), Jonny Quest, Jeannette (Alvin and the Chipmunks)
Kenshin (Rouroni Kenshin), Lisa Simpson (The Simpsons), Michigan J. Frog (Warner Brothers), Sheila (Dungeons & Dragons)
Bedtime Bear (The Care Bears), Sherman (Rocky & Bullwinkle), Stimpy (Ren and Stimpy), Mr. Magoo
Betty Boop, Sweet Polly Purebred (Underdog), Skeletor (He-man), Firefly (My Little Pony)
Each group of characters had a common letter. In order, the letters spell out: ANIME.