Keep in mind I might self cast this role. I want everyone to try their hardest though because you never know, you might surprise me.

Also, Simon is a young teen but is underdeveloped therefore has a higher pitched voice than he normally would at his age.

(Copied from Wikipedia)

The series protagonist, Simon (pronounced as See-mon) originally started off as a boy in the beginning of the story who suffered a low self-esteem due to his lack of parents and fear of earthquakes. Though physically underdeveloped for his age and ignored by adults and snubbed by girls, Simon is a valued digger in Giha Village. Simon is eventually befriended by Kamina, whose inspirational speeches start to give him enough confidence to muster his courage and take action in bouts of intense determination. Finding Lagann during his dig, Simon joins Kamina in going to the surface where he develops a crush on Yoko before learning she has feelings for Kamina. When Kamina died during the formation of Team Dai-Gurren, Simon is thrown into a maddened and pervasive depression, driving him to be overly aggressive in combat while isolating himself among the Team. But Simon's meeting with Nia helps him come to a revelation about his own nature, leading to him discarding his fears and doubts as he takes over Kamina's role as Team Dai-Gurren's leader.