Voiced by: Mitsuki Saiga (Japanese), Johnny Yong Bosch (English)
Rossiu Adai (ロシウ・アダイ,
Roshiu Adai) is one of the main characters of the anime and manga series, Tengen Toppa Gurren-Lagann. A boy from another underground village, Adai, in which the people worship the Gunmen as gods. A modest but intelligent person, he's often seen looking after the young Gimmy and Darry. When the twins are chosen to leave the village, he decides to go with them, thus the trio joins Team Gurren. Before he leaves, the village elder gives him a book that seems to withhold some secrets from humanity's past, with the task to find someone able to read it, as no one in his village can decipher its content. After Kamina's death, Rossiu temporarily begins piloting Gurren in his place, though initially has trouble, due to Simon's breakdown.
After the end of the war, Rossiu became Simon's second-in-command, always trying to make him act more serious about his duties as the ruler of Kamina City. However, it seems that his belief in Simon is not how it used to be, as he started to argue with him frequently. He also led a secret project to access Lordgenome's memories and learn from it the history behind him and the Anti-Spirals. After hearing all of the former Spiral King's story, and after facing the people's revolt when they heard the truth from Nia, Rossiu decides to use Simon as a scapegoat and overthrows him, putting him in prison, and sentencing him to death, an act that Rossiu is shown lamenting over by Kinon.
To protect the population from the impact with the moon to be provoked by the Anti-Spirals, Rossiu and his subordinates prepared a contingency plan by dividing it into two groups: one to take shelter in the underground villages, assumed to be safe by the government, and the other to board an ancient spaceship discovered in the lowest levels of the old Teppelin, the Arc-Gurren. However, when Leeron showed him that no life form, in the surface or underground, would survive the impact, which would render the planet completely uninhabitable for one year, Rossiu decided to change his plans, by filling the rest with animals and livestock, ensuring a chance of survival of them, and abandoning the rest of mankind. Earth was then attacked earlier than expected, and he had to escape with only half the expected refugees on board of the Arc-Gurren.
However, Rossiu's plans were once again foiled by the Anti-Spirals who had already set a large force awaiting to ambush the Arc-Gurren in space. Just when he was about to lose hope, Simon and the rest of Team Dai-Gurren came to his aid. One week after the Human Extermination System was stopped, Rossiu left a farewell message and set for his home, Adai Village, having decided to take his own life to atone for his mistakes. However, Kinon found the message and Simon rushed with her in Gurren Lagann to stop him. Rossiu takes the duty of watching out for Kamina City, while Simon and the rest of Team Dai-Gurren depart from Earth to the Anti-Spirals' homeworld, having Kinon and Guinble to assist him.
Source:
Wikipedia 
