Board Thread:Questions and Answers/@comment-44996737-20200206022310/@comment-44587829-20200209080350

The one thing i just noticed is Yuu's wings start from being 1 pair and then as story progressed, it is down to 2 pairs.

Yuu's black wings are mostly already confirmed by Kagami sensei to be Asuramaru's demon influence.

But likr you said, it is indeed still a mystery if Yuu as a Seraph himself is different to Yuu have a seraph inside him.