Two weeks after his last start of 2015, Rainbow Line began his second campaign in the Shinzan Kinen at Kyoto and finished sixth of the eighteen runners behind Logi Cry.
On 27 February at Hanshin the colt contested the Grade 3 Arlington Cup over 1600 metres on firm ground and started the 5.8/1 fourth choice in the betting behind Urban Kid, Ball Lightning (Keio Hai Nisai Stakes) and Hiruno Magellan.
Ridden by Mirco Demuro he raced towards the rear of the field before moving up on the wide outside on the final turn and staying on strongly in the straight.
In a "blanket finish" which saw the first five finishers separated by less than a half a length he prevailed by a nose from Dantsu Prius.

The Grade 2 New Zealand Trophy at Nakayama Racecourse on 9 April saw another very tight finish and Rainbow Line was beaten less than a length as he finished fifth behind Dantsu Prius.
On 8 May the colt was stepped up to Grade 1 class for the first time to contest the NHK Mile Cup at Tokyo and started a 40/1 outsider.
Ridden by Yuichi Fukunaga he exceeded expectations as he stayed on strongly in the straight to finish a close third behind Major Emblem and Lord Quest.
He was then moved up in distance for the Tokyo Yushun three weeks later in which he started at odds of 154/1 and came home eighth of the eighteen runners behind Makahiki.

After a break of two and a half months Rainbow Line returned to the track in August when he was matched against older horses for the first time in the Grade 2 Sapporo Kinen.
With Fukunaga in the saddle he came from the rear of the field with a strong late run to take third place behind the five-year-olds Neorealism and Maurice.
In October the colt was moved up again in trip for the Kikuka Sho over 3000 metres at Kyoto and started a 23.9/1 outsider in an eighteen-runner field.
After racing towards the rear for most of the way he produced an "impressive late charge" to take second place behind Satono Diamond with Air Spinel and Dee Majesty finishing close behind in third and fourth.
On his final run of the season in the Japan Cup on 27 October Rainbow Line produced his customary late run from the rear of the field to come home sixth of the seventeen starters, four lengths behind the winner Kitasan Black.

In the 2016 edition of the World's Best Racehorse Rankings Rainbow Line was given a rating of 116, making him the 158th best racehorse in the world.
Two weeks after his last start of 2015, Rainbow Line began his second campaign in the Shinzan Kinen at Kyoto and finished sixth of the eighteen runners behind Logi Cry. On 27 February at Hanshin the colt contested the Grade 3 Arlington Cup over 1600 metres on firm ground and started the 5.8/1 fourth choice in the betting behind Urban Kid, Ball Lightning (Keio Hai Nisai Stakes) and Hiruno Magellan. Ridden by Mirco Demuro he raced towards the rear of the field before moving up on the wide outside on the final turn and staying on strongly in the straight. In a "blanket finish" which saw the first five finishers separated by less than a half a length he prevailed by a nose from Dantsu Prius.
The Grade 2 New Zealand Trophy at Nakayama Racecourse on 9 April saw another very tight finish and Rainbow Line was beaten less than a length as he finished fifth behind Dantsu Prius. On 8 May the colt was stepped up to Grade 1 class for the first time to contest the NHK Mile Cup at Tokyo and started a 40/1 outsider. Ridden by Yuichi Fukunaga he exceeded expectations as he stayed on strongly in the straight to finish a close third behind Major Emblem and Lord Quest. He was then moved up in distance for the Tokyo Yushun three weeks later in which he started at odds of 154/1 and came home eighth of the eighteen runners behind Makahiki.
After a break of two and a half months Rainbow Line returned to the track in August when he was matched against older horses for the first time in the Grade 2 Sapporo Kinen. With Fukunaga in the saddle he came from the rear of the field with a strong late run to take third place behind the five-year-olds Neorealism and Maurice. In October the colt was moved up again in trip for the Kikuka Sho over 3000 metres at Kyoto and started a 23.9/1 outsider in an eighteen-runner field. After racing towards the rear for most of the way he produced an "impressive late charge" to take second place behind Satono Diamond with Air Spinel and Dee Majesty finishing close behind in third and fourth. On his final run of the season in the Japan Cup on 27 October Rainbow Line produced his customary late run from the rear of the field to come home sixth of the seventeen starters, four lengths behind the winner Kitasan Black.
In the 2016 edition of the World's Best Racehorse Rankings Rainbow Line was given a rating of 116, making him the 158th best racehorse in the world.
Rainbow Line