You can choose any one (or more) main character(s) and switch that person(s)'s gender(s) for some reason (like helping a friend for e.g.). Because of this gender swap, the main character(s) who switch gender(s) can get into all sorts of trouble like unwanted same and/or opposite sex affections, gender confusion, realization of the troubles due to gender, romance troubles due to gender switch, etc.

Bonus: Try having the main character(s) (both normal and after gender swap) get unwanted affections from both males and females. For example, if Ann switches to a man, then she gets unwanted affections from females for her manly side but gets unwanted affections from males for her normal womanly side too.

Double Bonus: Include one or more of the following ideas or scenarios:

• Pregnancy
• Period
• Nursing a baby
• Fighting physically
• Male/Female public restroom mayhem
• Shopping for clothes mayhem
• Unwanted teasing or affections from same sex people 

Have fun gender bending! I hope to enjoy the troubles your poor characters suffer from! :D