SUCCUMB ~What My Martial Artist Fiancee Really Desires~ / SUCCUMB ～武道家少女のホントの望み～

Our protagonist is just an average high school boy who does martial arts.
As it so happens, his fiancée Kaya is a legendary martial artist of immeasurable strength.
He doesn't measure up. Not at all.
He was happy spending his lovey days with her until she blurted out something alarming:
"Hey, are you the type to hate cuckoldry, or?"

Reading between the lines, it's clear. He must become stronger. As strong as her.
He sets to training. If he doesn't get stronger, Kaya might start sexing up other men who can satisfy her.
And for Kaya, what started out as a harmless joke might alight the true desire in her heart...