I don't necessarily think the physical appearance will necessarily be a problem since the more noticeable areas are the legs rather than the upper body and since japan is also an island nation being so close to the sea should help with the condition on its own. While i've never actually heard of a Japanese having ichthyosis i don't see necessarily how it could not happen as I dont believe one particular genetic race has an advantage against it over others. And conditions like asthma appear over there and people with ichthyosis can tend to have conditions like asthma as well.
Worst case scenario even if it is looked upon differently that will already be expected for me since I am a foreigner and japan is a very homogeneous country. I think that even if that is the case people will come to accept it at least to an extent as they have done here.