How do you evolve riolu with a sun ribbon?

To evolve Riolu into Lucario using a Sun Ribbon, you first need to ensure that Riolu has a high friendship level with you, as it typically evolves during the day based on friendship. Then, you must use the Sun Ribbon item, which is often found in specific Pokémon games or events. Once you have both the high friendship and the Sun Ribbon, simply use the item on Riolu to trigger its evolution into Lucario.