According to the search results, Ground-type moves are super effective against Raikou, which is a pure Electric-type Pokémon. Therefore, the best counters for Raikou are Pokémon that know Ground-type moves. Some of the best counters include:

• Groudon with Mud Shot and Earthquake
• Rhyperior with Mud Slap and Earthquake
• Garchomp with Mud Shot and Earth Power
• Flygon with Mud Shot and Earth Power
• Excadrill with Mud-Slap and Drill Run

It is important to note that Raikou is a legendary Pokémon and can be caught in five-star raids, so it is recommended to team up with other trainers to ensure you defeat it.