Although Rossiu in the English version is voiced by Johnny Yong Bosch I won't force you to imitate that.
However I do want a voice similar. I want it soft and a little higher pitched than a boy his age would have, someone like Simon but a little deeper.
(Copied from wikipedia)
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 the apprentice of his father, the village elder who governs Adai and performs its ritualistic method of dealing with over population by having people draw sticks with the winners sent up to the surface to die, Rossiu's mother being among those chosen. But when Gimmy and Darry were selected to leave the village, Rossiu is horrified to learn his father rigged it as they are orphans and decides to go with the twins and, thus joining 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 contents. After joining Team Gurren, he is often teased by Kamina, who calls him "Forehead Boy". After Kamina's death, Rossiu temporarily begins piloting Gurren in his place.