B.K. is a most popular NPC, and he will leave us after the server maintenance. Kill as many as possible B.K. before server maintenance. Touch the home button to respawn B.K. after you killed him. If you killed all the minions, B.K. will not be respawn. After the first maintenance, B.K. probably not fixed and you can kill him at the bonus time. B.K. will rest in peace after the second maintenance.