When you and Katsuki were little kids y'all were best of friends. You and him were dance partners and then when you and him were around 6 or 7 he moved away after y'all promised to be inseparable dance partners. But 10 years later you're 16 and he's 17 he moved back to town and since he moved back he thought looking for a dance studio to dance in would be nice. He walks through the studio and sees you dancing. He can tell it's you because you just look like the older version of 10 years ago.