The R Series of robots are enemies found in 2300 A.D. in Chrono Trigger. Collectively, they are the "boss" enemy the player must defeat in order to escape from the Factory.
R-64Y, R-67Y and R-69Y are among the six R Series robots.
The Factory Ruins
While Crono and his party attempt to exit the Factory, they are confronted by the R Series of robots. The six R Series robots inform Robo that he is defective, which is why he is helping humans and fighting against his own kind. So the R Series destroys Robo. The two remaining party members battle the R Series and defeat them.