How do you get raikou in Pokemon explorers of sky?

Answer 1

First, you must reach Master triple star rank. Once you reach that rank, the dungeon Southeastern Islands will become unlocked. After that, wait until you receive a challenge letter from raikou at Spinda's Cafe. Accept the challenge and defeat raikou at whatever floor he challenged you on. Once you defeat him and leave the dungeon without failing, raikou will join your team as a reward for defeating him.