The Hero's Girl Friend

Not to be confused with the Hero's Girlfriend.

Since the Hero is already likely a guy, the team needs to have a singular female in order to be sexually diverse. And because she's there, she might as well have some reason to be. The Girl Friend has numerous roles to choose from, such as...

As a female, she has an extremely low chance of having a worse moral compass than the Hero and usually is his Voice Of Reason if no one else on his team is.
 * Point-Proving Post-It (because politics, politics, POLITICS!)
 * The Archer (archery's for girls!)
 * The Fan Service Doll
 * The Hero's Girlfriend (if she gets too close to Hero)
 * The Nerd
 * The Healer
 * The Heroine (most commonly when she takes the spotlight as the Hero himself cannot)
 * The Hot Girl (In anime, she commonly uses the Power of Buu-Beez)
 * The Ladette
 * The Lamb