Because you like Mercedes Jones in Glee
Courteous, dangerous, and powerful, Kaname Kuran controls an entire court of vampires. Very, very pretty vampires. See them in Vampire Knight.
A super-soldier, Master Chief might be more machine than man. And for humanity's sake, thank God. See them in Halo.
The brilliant and well-adjusted Ender Wiggin is being groomed for the next generation of military leaders to fight alien invaders. See them in Ender's Game.
Stoic, cynical, and independent, Homura Akemi is an alluring enigma. See them in Puella Magi Madoka Magica.
Spike Spiegel is a bounty-hunter with a laidback style and lightning-quick moves. See them in Cowboy Bebop.