I have a feeling Kongou already caught Yamashiro's bluff when the latter improvised with that ninja gimmick. She was just merciful about it because she knows her love for the Kiddie is genuine.
Yama's gonna see Kaga eventually though, and when that happens, 'hoo boy~
Kongou has adopted Yamashiro, but those stains around her mouth are....
"It is by will alone I set my cannons in motion. It is by the juice of Ceylon that the burning acquires love, the lips acquire stains, the stains become a warning. It is by will alone I set my cannons in motion."