Alright so I just thought of a really random thing.
Both Klaus and Gilgamesh Wulfenbach are really good fighters. Like, they both managed to whup Jäger butt and throw Othar through a window.
And then I imagined lil small kiddo Gil and Klaus play-fighting. TINY BABY MUNCHKIN CHILD GIL TRYING TO TAKE DOWN HIS TANK OF A FATHER. BY AMBUSH WHEN HE’S IN HIS LAB. KLAUS GIVING HIM A SMALL BIT OF A CHALLENGE (at the very least it’s valuable learning experience) AND THEN LETTING HIM WIN.