Once you have beaten the other 7 kanto gyms talk to him on cinnabar island and he will go there
go to the 5 gym
the last gym leader is Blue.When you go to the seventh gym leader Blaine you should see Blue and asks you if you have 7 badges then you beat Blaine and go to Blue and he says to meet him at his gym
The last gym leader Blue is first at cinnibar island talk to him so that he returns to his gym go to viridian city and go into the gym battle Blue to receive the last badge.
To find blue defeat all of the gym leaders and then go to cinnabar island blue will be there and will accept your challenge if you have defeated all of the gym leaders. Then go to viridian city gym and get through all of the trainers. After this you can also battle red.
After you obtain the Blue Orb you go to Sootopolis City and go into the cave behind the Gym
You have to get the other seven Kanto gym badges, and then show those badges to Blue. Blue is on Cinnabar Island, and he will not leave to go to the Viridian City gym unless you show him the seven Kanto badges.
You go to cinnabar island and talk to blue he then goes back to his gym
you got to beat all the Pokemon gym leaders in kanto other then blue,then talk to him
you have to get all of the other gym badges in kanto and then go to Cinnabarr island and talk to blue. then go to viridian city and go in the Pokemon gym!
go to cinnabar island where blue is. talk to him. hes the 8 gym leader. he will go to the gym once u talk to him when you have 7 gym badges
Go to Cinnabar island and talk to Blue. He'll agree to go back to his gym and battle you.
the eighth gym is in virdian city, talk to blue on cinnibar island and he will go back to his gym.