Friendship is important in Pokémon Brilliant Diamond and Shining Pearl, as it will help your Pokémon to perform better during battles. There are a couple of ways to improve friendship in the game, and one of them is with the Soothe Bell.
A Pokémon equipped with the Soothe Bell will gain 50% additional friendship, rapidly increasing their ranking up. It can then be given to other Pokémon for the same effect.
Where to get the Soothe Bell
The Soothe Bell can be found on Route 212 in Pokémon Brilliant Diamond and Shining Pearl. Here, you will find the Pokémon Mansion. If you go inside, you will find an NPC maid in the second room on the left. Speak with her and she will give you the Soothe Bell for free.
Once you have the Soothe Bell, you can give it to a Pokémon by opening the bag in your inventory, selecting the Soothe Bell, and the Give option, and picking the Pokémon you wish to give it to. You can only have one Pokémon holding the Soothe Bell at any one time, so pay close attention to them so you know when you have maxed out their friendship level.
If you want to know who will benefit from it the most, and who needs the friendship boost, there are a number of ways to check your friendship level in Brilliant Diamond and Shining Pearl.