Aki found this article snippet from Great Mechanics DX17 (summer 2011 issue) and translated it. It’s an interview with (most likely) producer Kazuhiko Tamura from Sunrise and it mentions an upcoming addition to the cast, Kotetsu’s older brother.
Well, Kotetsu emigrated [to Sternbild]. Right now, his mother is looking after his daughter, Kaede. But there is one more person watching over them – Kotetsu’s older brother, who’ll appear in the show soon. Kotetsu doesn’t want to reveal his hero identity, but his brother and mother both know about it, the only one in dark is his daughter.
We’ve seen a few mentions that he’s supposed to appear in episode 14 but we can’t confirm that without a source.
(Episode 12 post coming as soon as we can sort our thoughts on it. Geez, Sunrise…)