you dont, its only in HG and SS (P.S. Its spelled Raikou)
raikou cannot be caught on Pokemon ruby
to catch Pokemon you have to obtain raikou palls
Raikou is only found in firered and leafgreen if you chose squirtle as your starter Pokemon. Or you can get the purified raikou from Pokemon colosseum.
You cant get raikou in Pokemon diamond or Pokemon pearl.But you can get him in a gba Pokemon game and transfer him to your Pokemon pearl or diamond!
You can't find raikou in ruby.
Entei, Raikou - Lv. 40Ho-Oh (HG) / Lugia (SS) - Lv. 45Suicune - Lv. 40Lugia (HG) / Ho-Oh (SS) - Lv. 70Latias (HG) / Latios (SS) - Lv. 35 (Lv. 40 in Event)Articuno, Zapdos, Moltres - Lv. 50Mewtwo - Lv. 70Kyogre (HG) / Groudon (SS) - Lv. 50Rayquaza (if you have Kyogre and Groudon) - Lv. 50Read more: What_legendary_pokemon_are_available_in_Heart_Gold_and_Soul_Silver
Raikou isn't on Pokemon Pearl, if you want it you must transfer it from another game
you can't. raikou is a generation 2 Pokemon. Pokemon blue is a generation 1 game. so it is impossible!
You cannot catch Raikou in Pokemon Diamond and Pearl. To get Raikou in Pokemon Diamond and Pearl, you must trade for one from Pokemon HeartGold and SoulSilver where it can be caught or transferring from Pokemon FireRed and LeafGreen.
raikou is better
You go to a mountain and catch raikou