Ugh... I have to say this. Or else.
Twins are (almost) identical only if they are both girls or both boys. If they are a girl and a boy, they can be as similar as two non-twin siblings. That's because "identical" twins come from a split ovule (that is, same DNA: same chromosomes XX or same chromosomes XY) and non-identical twins come from two different ovules (different DNA; could be two girls, two boys, or girl and boy).
This is not hidden information. People learn this at primary school. So why why why do writers, mangakas, film makers, why do they omit this fact? I don't buy they ignore this!
aah now that I have let off steam I feel I am open to read any nonsense.