Lucario is a Pokémon that everyone would like to add to their team in Pokémon Brilliant Diamond and Brilliant Pearl. But you will have to go to great lengths if you want to get a Lucario. You will have to do this with a Rilou, the initiated evolution of Lucario. Here's what you need to do to evolve Rilou in Lucario into Pokémon Brilliant Diamond and Brilliant Pearl.
For Riolu, once you hatch him when you get the egg from Riley, all you have to do is take care of him and raise his friendship by at least one level. The best way to increase your friendship with Riolu is to take Riolu out and hang out with him. You can do this if you've visited Amity Park and walked around with another of your Pokémon.
After walking for about a minute, you will need to evolve Riolu. It only takes one friendship level and one experience level for Riolu to evolve into Lucario, so you can evolve it at a reasonably low level. If you want to increase the friendship Riolu receives, make sure she is wearing the Soothe Bell item.
You will need to do this every time you hatch a Riolu egg and evolve it into a Lucario. The process isn't complex, but knowing the exact way to do it is key.