On 18 March 2018 Rainbow Line began his fourth campaign in the Hanshin Daishoten over 3000 metres.
He started the 4.6/1 third choice in the betting behind Clincher (Kyoto Kinen) and Albert (Stayers Stakes) in an eleven-runner field which also included Satono Chronicle (Challenge Cup) and Curren Mirotic (Kinko Sho).
After being restrained towards the rear as usual, Rainbow Line moved up on the outside on the final turn, hit the front approaching the last 200 metres and recorded his first win for more than two years as he came home a length and a quarter in front of Satono Chronicle with Clincher in third place.

At Kyoto six weeks later Rainbow Line made his second attempt to win the spring edition of the Tenno Sho and was made the 5/1 second favourite behind Cheval Grand.
Clincher, Satono Chronicle, Albert and Curren Mirotic were again in opposition while the other eleven contenders included Ganko (Nikkei Sho), Chestnut Coat, Tosen Basil, Mikki Rocket (Nikkei Shinshun Hai) and Smart Layer (Hanshin Himba Stakes).
The outsider Yamakatsu Raiden set the early pace with Rainbow Line settled well back in the field.
Cheval Grand gained the advantage in the straight but Rainbow Line threaded his way through field after being switched to the inside by Iwata, caught the favourite in the final strides and won by a neck.
Immediately after the race the horse was found to be lame, having sustained an injury to his right foreleg and was taken receive treatment at a veterinary facility rather than taking part in the victory ceremony.
Iwata said "While our rivals were making early moves in the backstretch, my mount waited patiently, and I knew he had the needed late kick to reach the front before the wire.
I'm worried about the horse.
I just hope he’ll be able to run in the next race" while Hidekazu Asami commented "It's great that he was able to win but I'm concerned about his condition.
I hope to give him the best care as possible".

Rainbow Line was unable to return to the track following his injury and was retired from racing at the end of the year.

In the 2018 World's Best Racehorse Rankings, Rainbow Line was again given a rating of 118, making him 78th best horse in the world.
On 18 March 2018 Rainbow Line began his fourth campaign in the Hanshin Daishoten over 3000 metres. He started the 4.6/1 third choice in the betting behind Clincher (Kyoto Kinen) and Albert (Stayers Stakes) in an eleven-runner field which also included Satono Chronicle (Challenge Cup) and Curren Mirotic (Kinko Sho). After being restrained towards the rear as usual, Rainbow Line moved up on the outside on the final turn, hit the front approaching the last 200 metres and recorded his first win for more than two years as he came home a length and a quarter in front of Satono Chronicle with Clincher in third place.
At Kyoto six weeks later Rainbow Line made his second attempt to win the spring edition of the Tenno Sho and was made the 5/1 second favourite behind Cheval Grand. Clincher, Satono Chronicle, Albert and Curren Mirotic were again in opposition while the other eleven contenders included Ganko (Nikkei Sho), Chestnut Coat, Tosen Basil, Mikki Rocket (Nikkei Shinshun Hai) and Smart Layer (Hanshin Himba Stakes). The outsider Yamakatsu Raiden set the early pace with Rainbow Line settled well back in the field. Cheval Grand gained the advantage in the straight but Rainbow Line threaded his way through field after being switched to the inside by Iwata, caught the favourite in the final strides and won by a neck. Immediately after the race the horse was found to be lame, having sustained an injury to his right foreleg and was taken receive treatment at a veterinary facility rather than taking part in the victory ceremony. Iwata said "While our rivals were making early moves in the backstretch, my mount waited patiently, and I knew he had the needed late kick to reach the front before the wire. I'm worried about the horse. I just hope he’ll be able to run in the next race" while Hidekazu Asami commented "It's great that he was able to win but I'm concerned about his condition. I hope to give him the best care as possible".
Rainbow Line was unable to return to the track following his injury and was retired from racing at the end of the year.
In the 2018 World's Best Racehorse Rankings, Rainbow Line was again given a rating of 118, making him 78th best horse in the world.
Rainbow Line