I like it so far remind me quite a bit of
Imperium (which is good) be careful to not go too much in the same way.
LordCorwin idea sound pretty good because, it does look a little bit too easy right now.
As for the male, i'm not a fan of MM content and transforming someone too easily feel like a plothole for me.
If you want to put transformation in your game, i think that a slow transformation of weak minded male into female (with a choice at the start of the game which change pics of those betaguys into either sissy/trap or petite girls) and being discreet around strong one would be a good way of getting at it. Then again being able to transform assshole in stupid bimbo is quite satisfactory, so maybe in the late game being able to change the strong guy who where bothering us at the start since our power are stronger can be nice.
If you'd rather keep your game transformation free, i think that Fulcrum got it, meaning that you can use your powers in a way to trick other people in thinking that what you are doing is perfectly normal (with a progression of course, at first you should be alone with the person that you want to control and after you could start to control them in small thing like being dressed like slut in broad day light and people not paying attention to it and in the endgame being able to make them suck you off on stage while you do a speech)
A spell for all did it by making you unlock a spell to create a "bubble" around you and you target.
For the "a stone give you power" thing why not ? but maybe devellop it further by asking yourself some question on where you want to take it in your story.
I see it two way,
First, the MC can lose his stone which mean it can be stolen, there is other stone users and you can absorb their power if you get their stone (sound like imperium but you can treat it differently). The stones got different power (mind control, self-improvement, transformation of other people ... you name it) if you end against someone who get the same power as you it will strenghten it and strong user can have multiple powers (your sister masturbating furiously when you come home and hanging half-naked in your house might be because someone is corrupting her).
Second, the MC is the only one who got power and get stronger either by fully corrupting people in his will-less slave or meditating/training with his stone which can unlock new power or evolve those that you already have, maybe with a progression bar and some event who can unblock a new path in your power, lets say that the MC is training his power on his slightly corrupted sister and when he driftaway thinking that it would be nice if she were blonde Boom next morning she is, he can induce change on a person by the power of his mind (at first just small physical change and then transforming male for example).
On a side note, why a stone ? why not a ring or a pendant ? and what is he doing on a construction yard ? i feel like your way isn't wrong but badly bought up, it does feel a little bit too much random.
Well i hope that you like my way of seeing things and that i helped you get thing clearer on what you want to do with your game but remember that, that is
your game and you should do what
you want, i'm just speaking my mind here.
And you wont be able to satisfy everyone, if you try too hard your game will be weird and you will be less likely to finish it.
Have fun doing it and we will have fun playing it.
