Board Thread:Questions and Answers/@comment-142.116.101.203-20170605024627/@comment-142.116.101.203-20170606143538

So the person in the window was most likley her brother.

Kirito is taller than Asuna by about 10 centimeters, but the person in the window looked a bit taller than that.

However we are never given details on what Kouichirou looks like.