After clearing the desert to help Fiona grow her forest, Fiona needs a helper that can live to see her forest grow and prosper. Robo, being the considerate robot he is, becomes that helper, and for four hundred years, grows and tends Fiona's forest. After four hundred years, the group met up with him in Fiona's shrine. Since Robo hasn't seen him for four hundred years, he decides that they should have a reunion. For their reunion, they sat around the campfire in the middle of Fiona's grown forest and discussed about the cause of time gates. Robo believes that the time gates are not caused by Lavos, but are caused by someone else, who wants his most terrible memories to be seen by the group.
After the others fall asleep, Lucca takes a time gate to the time in her past that she would like to change. After she changes her past, Robo comforts her by giving her Green Dream, an item he made using forest sap.
When Robo and the gang head into the Geno Dome, the Mother Brain welcomes them. After the group proves their talents in battle to Mother Brain, they learn that Mother Brain is using the Geno Dome as a place to destroy humans, so the group decides to stop her. After getting the two dolls to unlock the doors of Mother Brain's room, Robo and the others meet up with a pink robot with a green ribbon on her head named Atropos, who wants to destroy the humans in Robo's group. Sad in the change that Mother Brain committed onto his girlfriend, Robo decides to fight Atropos to protect his human friends. After fighting Atropos, she returns back to her true self and before her memory bank fails her, she gives Robo her green ribbon. After her death, the group open Mother Brain's room with the two dolls. When Mother Brain sees them in her room, she tries her last efforts to persuade Robo to join the robots to destroy the human race,
but he refuses. After he refuses, Mother Brain fight the group and loses. Since Mother Brain is gone, the Geno Dome becomes inactivated and the birthplace of Robo can never be enter again.