Board Thread:Questions and Answers/@comment-27709088-20160209062008/@comment-5527544-20160209145512

No one knows why Seven looks so different in X, it could be like an art style, different artists can draw the same character differently but it's still the same character. i.e. the change is cosmetic for the series and in-universe, he looks the same as always.

Another theory is that Seven's body just adapted to the new universe's physics or it was a side effect of his method of travel.