Jezzi Belle wrote the right words, and I agree with her.
Silvia.

Way to easy an acceptance of being feminized without being informed  particularly when sex with men was part of the program.  To make this believable, I think some background needs to be introduced to the effect that he was secretly investigated by the school before being offered the position and found to be gay or Bi or at least seemed willing to experiment with alternate lifestyles, or that the drugs he was taking were brfainwashing him into easy acceptance.   If not brainwashing, even if he liked it, I would think he'd be mad as hell about being tricked.   From the school's point of view, without the background checks or brainwashing, they are putting a lot of time and money into a very, very risky venture.

A new setting for an old tale, competently written.

However there are a few points to quibble about. "Geisha" is a Japanese custom and profession. Koreans, still highly resentful of the 40 year Japanese period culminating in the "pillow girls" of WWII, would most definitely not have their upper class children participating in that program. A change of scene would eliminate that problem.

The writing, particulary the sentence structure, would be improved by some variety. The story pace is so consistent that it loses tension.

The portrayal of emotional state is weak. It's not that "Sophia" needs to be portrayed as more emotional, but it's described, rather than portrayed. Consequently the heroine feels two dimensional rather than drawing the reader into the situation.

For example, the agreement to be transformed does not vividly portray any qualms, fears, misgivings, or changes in emotional state. You go from weak indignation to acceptance without a pause. If you didn't feel comfortable describing that change of mind, it would be more effective to have the proto-Sophia predisposed and intrigued by the possibility.

Similarly I have virtually no impression of Sophia's image, her changes, or her evolving shape. Like her personality, Sophia is sensed through a fog. The reader doesn't have to know whether there's a dimple in her cheeks, but something would help. The oft used description of a transformee coming to grips (I know that's an awful pun) with managing and caring for her new body works because it allows for interplay of physical and emotional description.

It's an easy, competent read, an interesting situation, but so far it lacks a strong emotional hook to make the reader care what happens to the heroine.