So my personal thoughts are the general idea is great, lots of good thoughts put into the project, my recommendations however are to allow the melee weapon to be upgraded, (potentially adding a knife or changing it to a spear) and to change how syahata looks depending on the level of corruption that she has.
such as during her second stats where she shows her pantys during the surrender, possibly having her top be lose could be a good thing to do, and at the final stage where she is offering herself up, removing all underware and having her shirt be completely open (similar to the game over screens) would be a option (possibly make it the players choice as to if she ends up doing this or not via a pop up and or option in the pause menu)
While presenting further work it would help with the immersion level of the game.
As well as the possibility to wash out/remove eggs and cum from syahata would also be a good possibility. With the eggs you could make it masturbating loses them, so you have to masturbate multiple times to get them out prematurely. While with cum you have to either use a clean sink or bottled water to remove the seman from her.
With regards