I'm not familiar with Gundam Seed but I looked this up and although they are indeed twins, it seems they don't know until later on and I'm assuming this can be considered a spoiler for the series, do you think it's a plot device not to know they are related?

I really would rather if you look for another pair, sorry, because we're trying to keep the deck spoilers free. Unless you tell me that the viewers know they are twins from the beginning even if the actual characters don't know.