The game is looking good, but somethings that could improve (i will not comment on grafics for now as i think you probably will improve it for the scenes latter on), but on to the plot and gameplay suggestions:
Plot:
-I think we should have more of Tali's imputs even if they are just thoughts in the interactions she have, it should give us more insight on what kind of character she is and who she can become;
-We should change slightly the outcome of the sucession fight IF Tali trigger some especifics requirements (story lesson + scroll 2, maybe interactions with the Queen and Alva can change slightly their comments and opinions on the Prince's plan as well), maybe have her try and come up with a countermeasure for it. She was sure her brother would do that and did nothign but wait FOR 7 years, for God's sake be more proactive;
-As a mentioned the 7 years jump in the latter section, let's talk about it. Basically it's too much time for literally nothing to happen. Here comes some suggestions:
1. Maybe let's us choose how she interacts with her brother, the Queen, her father, Alva and maybe some other future interectable/romanceacle character.
2. Let us choose some type of magic/craft/even weaponship to focus, therefore we have an up hand on some trainings, scenes, interactions and even romance later on (don't know which type of game you are planning, but this should offer something).
3. Let us choose how Tali acted about her new appendage: Was she curious? Did she 'got it on' with some maid? Was she grossed out by it and never tried anything? Basically, give us something to change her behavious about her sudden change.
-Give us some free lore for those interested in learning more about the game, many games have THAT library in the beggining in which you can learn about the game, many people (me included) love to learn more about rpg games, plot are usually very important to those (especially the character-driven and story-driven ones). These are entirely restricted to plot and lore and should have minimal if not zero impact on the gameplay.
That should sum up what i think about the plot, now about the gameplay:
-Making the fights harder is a given, but it shouldn't deprive those that don't like fights too much fun. So winning should offer you rewards (anything really: from extra xp, to scenes, to itens/equipament and even additional/secret characters interactions or scenes) while losing would either result into a plot point, a game over (if it's a MUSt win fight) or just the loss of the aforementioned rewards.
-Make sure that EVERY choice have an outcome, don't just offer diferents choices that won't give you anything, it removes the dinamic in the game.
Example: The choice of lesson you have (history, scriptures or fighting should offer different outcomes not just xp and a comment from Tali latter on). The question you ask the Goddess (change the Goddess behaviour towards Tali, maybe even 'give' her a bigger or smaller 'blessing' depending on the choice and some unique buff maybe, nothing too extraordinary).
Basically, every choice should give you some reward while depriving you of something that the other choices gave (could be possible get what you didn't later on by different choices if you want
-I know this will come up latelly, but let us choose at least one element for Tali to be more leaned towards (maybe different elements give different bonus to statuses? Earth = more armor/magic resistance. Fire = more damage. Wind = more movespeed+dodge chance and resistance to status ailments. Water = more mana and extra healing effects. And so on, i know that Tali herself said she wasn't good with elemental magic, but she should have an element she is more natural with, it sounds normal.
-The fight of the sucession shouldn't be a sure lose one, at least for the first engage with the assassins. As i said, reward the players that take combat more seriously, give something out of it even if relationship points with the brother or something seeming not too important while still charming the players into trying their best to fight for the win.
And i think, that sums up my ideas. Really, those are just suggestions take some inspiration (or even copy if you found some of then good enough) from then or not, it doesn't matter as i still look foward for more. Loved Roll the Dice concecept, hope to see some mechanics, characters or so in here, keep the good work and it shall reward you!
P.S. As i said, i won't comment in the scenes and the sex nature of the game yet as i'm sure you didn't finish your ideas for them. Will comment when more comes into light~ Love me some futa/trans, hope it turns good, dirty and 'femaledickfull'~