I saw that you asked for suggestions so here you go. The concept is already interesting to plenty of us and flexible with a guy being transported to another world so It's easy to bounce around whatever story you like. 1. Have variety in personality of the futanari, some can be controlling like the princess sure but others can be a loner, a sweetheart, a hard ass, by the numbers and dutiful, shy and hardened shell, dominatrix, or just a best bud that shows some interest romantically. 2. Do you have a goal in mind in regards to an ending because while it certainly takes a lot of work having multiple character routes and choices afforded to the player makes it more personal to us as the player. 3. Adding dom/sub/loving/ romantic choices allows us to see more sides to the characters and lets we the player create our own story and perspective on who our protagonist is and where we plan to end up. At the side of the princess being bred every night? As a slave being forced to work as a whore to survive? In a loving marriage with our futanari alien wife who's genuinely amazing. As the leader of the futanari and able to fuck whoever we choose. These are all possibilities several would like to see through. 4. Decide the tone of the story, lighthearted and playful which seems to be the initial angle or more serious with time? Do you want a more involved and dynamic narrative? 5. Finally I'd suggest a way to keep our information on characters we know as well as our own stats always convenient in a menu. As well as hints to progress the story in a direction of our choosing depending on what direction you go. I hope some of what I've written down is helpful in any way and as a fellow futanari enjoyer I wish you the smoothest development with Futanari Universe Ivan