Friendship

Friendship is an aspect in the Pokémon games. It is literally the bond between trainer and Pokémon. Friendship can be gained by winning battles, using certain items, and healing the Pokémon. The higher the friendship, the more the Pokémon likes the trainer. All Pokémon can reach high friendship. However, strong Pokémon and Legendary Pokémon are hard to befriend.

In Game
In HeartGold and SoulSilver, the aspect of friendship can be viewed by interacting with the Pokémon in front of the party. When friendship is high, Pokémon can show signs of affection towards their respective trainers. Some of these signs can be strong. Friendship can determine the power of Return or Frustration. Friendship can evolve certain Pokémon.