First of all: Please change the guy's artwork. He looks far too child-like. That's just eeehhhwww! Lust and Power is good a example for a way a male protagonist in a M/S game may look like. The artwork for the mom and the background are nice, but the guy is just extremely disturbing.
A few ideas for a story:
- Parents divorce after mom has an affair [ideally with another woman, add some lesbian action]. Mom loses everything within the process, so she seeks help from son [and his girlfriend/wife]. Which he offers, but at a price... This would be a good story for a domination/corruption game.
- A global fallout has struck the earth and the protagonist and his mom are the last human beings on the planet. For humanity to survive, the protagonist has to fuck his mom.
- When the son goes to a brothel, he discovers that his mom works there. He blackmails her into using her services for free.
- Son convices mom to leave abusive father and offers her a new home. She shows her gratitude.
- Mom gets kid-napped and dominated by a succubus. Son rides to her rescue in shining armor. The demon decides to corrupt them both.
- Son comes home from work early and discovers that his mom and the ladies from the neighborhood are having lesbian orgies in their husbands absence. He decides to blackmail them and form a harem of sexy milfs starting with his mom.
- Dad dies and the son inherits everything, his mom gets nothing. He takes advantage of the situation and demands sexual favors.
- Mom is sick and tired of her boring stepford wife life and leaves home to seek some change. Her overly virtuous son follows her and tries to convice her to come back. She has other plans though and seduces him... This would be the corruption theme from the other side, with the mom as protagonist.