Rossiu Adai (ロシウ・アダイ Roshiu Adai?) is one of the 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.
In part one of the series, Rossiu has slightly long black hair pulled back in a pony tail with a bang on the right side of his face. One might describe his head as being a little melonish and too large for his body, a feature that prompted Kamina to give him the nickname "Forehead Boy". He has thick black eyebrows and black eyes. For the entire first part of the series he is seen wearing the modest religious garb of Adai village. His clothing includes loose white-blue pants tucked into tan boots and a white poncho/cloak with a high collar and two rectangular blue markings on the left side. He often wears a flat and sullen expression and rarely shows emotions other than anger or frustration, smiling once or twice.
Rossiu's general appearance changes a bit in part two of the series,most of the changes being that of clothing. The color scheme is the same, but he now has a more commanding appearance, largely due to his military-like clothing. He wears a white coat that goes down close to his ankles. He wears white pants and boots, and two orange shoulder pads, the left one having a darker orange stripe down the middle. There are two orange stars on the left side of his chest. He still has the same pony tail hair, only slightly longer. Rossiu also seems to have grown into his melon forehead. In this part of the series, his expression remains as blank as ever, showing actual emotion even less than usual. However, he does seem to have a slight smirk when exhibiting his stolen powers.
Rossiu is a devout and good-natured young boy in Part 1. He is kind to strangers as he is friendly with Simon, Kamina and Yoko upon meeting up. He is modest as he tells a voluptuous Yoko to cover herself. He is also very protective of his faith, nearly challenging Kamina to a fight when the latter claimed that their holy idol was mere a Gunman. He also seems to have a father-son relationship with the priest of his village, trusting him completely before learning the truth about Gunmen and the surface. Upon joining Gurren Laggan, he became a big-brother figure to both Gimmy and Darry as well as a reliable member of the team. However in Part 2, his role changes rather significantly. He becomes more cold, underhanded and extreme. After becoming Chief Advisor, he uses his position in government to keep people from going back underground to monitor the human population. Once it reached one million, triggering the Anti-Spiral attacks, Rossiu quelled public outrage by blaming Simon and locking him up, effectively usurping power from the latter. He develops a twisted sense of justice and sacrifice, condemning Simon to die for the moon falling and saying Kamina's death was "for the best". Rossiu would even attempt abandoning a portion of humanity to die on Earth after discovering from Leeron's calculations that the surface would be uninhabitable for a year. Despite his machevellian tactics, Rossiu believes what he is doing is for the greater good of humanity but ironically he became no better than Lordgenome. After Simon stopped the moon from falling, Rossiu felt so much shame from his actions that he planned to kill himself in his home village. However, after an intervention with Simon, he changed his ways and dedicated his life to being a better leader and friend. After 20 years, he still kept this promise as a leader spreading peace throughout the galaxy.
Before events of Gurren-Lagann
Raised in Adai village, Rossiu was a deep believer in the fake religion the elder had enforced on the village. Due to the village's law that only a certain number of people could live in the village at one time, Rossiu's mother was exiled from the village and died on the surface.
Beast Man War Arc
When he first meets Kamina, Simon and Yoko, he is not pleased by their appearance and attitude. He does not believe they could be from the surface, which is known as the land of Gods by his village. After the elder fights using their totem gunmen and the truth behind the fake religion is revealed to him, Rossiu leaves the village with Gimmy and Darry to join team Gurren. After Kamina's death, he becomes the pilot of the Gurren, but has trouble with it due to Simon's breakdown. Despite his lack of composure when doing so, he is shown to be a reasonably skilled pilot, dodging a large number of missiles during the battle against Cytomander's Dai-Ganten. During the battle with Lordgenome, Gurren is detached from Lagann during a botched capturing attempt and Gurren is tossed to the side. While Lordgenome and Simon fought using their spiral power, Rossiu sits in Gurren and watches (similar to Viral ).
Anti-Spiral War Arc
Now the second in command, he constantly attempts to remind Simon of his duties as leader of New Kamina city. 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. Rossiu's plan does not work, however, as the anti-spirals had anticipated this and had Mugann ready to ambush them. Nearing despair, Rossiu is saved by Simon and Team Dai-Gurren who enter space and save the ship. However, when the earth becomes dangerously close to destruction, Rossiu orders Gimmy and Darry to pull the Arc Gurren-Lagann out at the last minute, telling them to do it as his final order. Thankfully, Simon managed to convince Nia to move and the earth was saved. Unable to cope with his decisions, Rossiu fell into despair.
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. As Rossiu was about to pull the trigger, Gurren-Lagann appeared in a rift created by teleporting. Rossiu attempted to fire, but hesitated when he heard Kinon's voice. This allowed Simon to punch Rossiu, giving him the words of encouragement Kamina once gave him. Rossiu snaps out of his depression. Later on, 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' home world, having Kinon and Guinble to assist him. After the final battle against the Anti-Spirals, Rossiu was the priest for Simon and Nia's wedding.
In the epilogue, he is seen still holding the position of commander-in-chief, as Simon did not reclaim it. In the epilogue, Leeron refers to Rossiu as "President", telling him only he could've achieved what has been achieved, with Rossiu disagreeing, stating Simon could've done it as well, wondering where he is, but believing he's watching over them.
- The name that Kamina refers to him as in the primary series "dekosuke" is a remark regarding the large size of Rossiu's forehead. The name "dekosuke" roughly means "big forehead". In the dub, Kamina nicknames him "Forehead Boy."
- Rossiu narrates the episode previews for episodes 17 to 22, which each have one of his lines within the episode used as the title for it. They are shown by a computerized font.