How about a typical harem story our of a anime or hentai novella, involving different types of WG, temporary transformations, a beach episode, etc., etc.
The Twist: It’s revealed that the dude is actually a tomboy girl.
At first, they’re weirded out (except the older ones) until they come around to thinking that its ok (maybe some have had bad relationships with men, some think that she’s more sensual than a man, maybe they find out that they swing both ways).
The double plot twist reveals that she’s super curvy as well. From there, more crazy shenanigans happens.