I see that you are open to quite a few fetishes, ok gonna give my recommendation:
-First we need to get a concept, who is the MC? what is his situation? challenges? will give a simple example: "In this game you are a 3rd year of economics studying in Axholf University, you were currently living alone but now that your little sister has 18 she is going to your university too and because of money issues she will be living together with the MC, manage your relationship with your sister, university friends and fight off bad situations, get a girlfriend and be aware that no ones tries to get her away from you, what will you do? achieve a difficult harem, get into an incestuous situation, or perhaps you will fall and lose what you love?"
-Second the main choice you should have is what fetishes do you want to add?, some fetishes can give place to interesting combinations, for example take NTR, it isn't the same to be done by a male, female or shemale just to say a few examples.
I would personally find interesting NTR done by female, shemale or futa. The black male one is a bit overused in my opinnion.
But well the fetishes will determine how the game develops. Basically choose the ones you like the most. I'm one of those that love to always have the opposites, basically if femdom I like maledom too, if netorare I like netori...
Following the example "femdom, maledom, lesbian, male protagonist, NTR (netori and netorare), foot fetish, BDSM, anal, trap, pregnancy, sissification, oral, blackmail, futanaris" would be the tags
-Third you start to think about how to implement it on the game: Let's talk about femdom for example, you imagine the situations that you like and think about how to accomplish it. Let's say that you decide to add two stats that influence the femdom, like respect and dominance. It would help you to make two types quite easily, high respect and high dominance means a dominant relationship, low respect and high dominance means a slave/servant relationship.
You want something else? then for example you could add fetishes that a girl may unlock, like BDSM, sissyfication... to make that part more complex.
Then you think about what increases or decreases those stats. Will they be affected by random chance? player's choices? interactions? events?.
This is truly extensive and requires a lot of writing and thinking before working on the game, following what I said before will give you a tiny part of the document you should design:
Stats:
-Respect: You will start the game as respected, the different respect levels are:
*No respect: 0 to 20
*Little respect: 21 to 40
*Respected: 41 to 60
*Very respected: 61 to 80
*Idolized: 81 to 100
Depending on how respected you are, your sister will treat you better or worse and it will affect that she is more obedient or won’t care about you.
For example if your sister has no respect from you she may steal money, insult you, taunt you with the fetishes she discovered you had or making you remember embarrassing or bad situations that happened in the past.
Even more she won’t obey you or hear your opinion about her issues, she may take a boyfriend or girlfriend home to have sex, get interested in bad things…
On the other hand, being idolized will make her ask you about many situations and obey what you say, it will give the player quite a lot of control over how she acts.
-Dominant/submissive: This will have an effect mainly on sexual interactions, if the sister is dominant she will tend to tease you, be more aggressive on sex or perhaps even force you to have sex (if she has an incest fetish).
Submissive on the other hand will tend to get you to show your “hidden wolf”, basically she may make a mistake to be reprimanded, taunt with your fetishes so that you are sexually aggressive or even service you to get you in the mood.
-Fetishes: The sister will develop fetishes gradually during the game, those are divided on first, second and third levels. Basically certain combinations of fetishes or stats will generate new fetishes.
1º level fetishes:
ºNeutral ones:
- Anal
- Oral (giving or receiving)
- Cum addict
- Incest
- Futa lover
- Masturbation
- Voyeurism
- Exhibitionism
- Porn addict
ºDominant ones:
- Foot domination
- Light Sadism
- Strap-on
- Non-consent
- Orgasm denier
- Sissy lover
ºSubmissive ones:
- Light masochist
- Bondage
- Servicing
- Gangbang lover
- Being forced/raped
2º level fetishes:
- Masturbation + Exhibitionism + medium sluttery = Public masturbation
- Anal + cum addict = Anal slut
- Oral + cum addict = Oral slut
- No to little respect + Foot domination + Incest + A little dominant = Foot master
- Light sadism + strap-on + non-consent + orgasm denier = Dominatrix
- Light masochist + bondage + servicing + being forced = Slave
3º level fetishes:
- Public masturbation + anal slut + oral slut + high sluttery = Public slut
- Foot master + High domination = Foot queen
- Dominatrix + sissy lover: Sissy dominatrix
- Slave + anal slut + oral slut + high respect + high submissiveness = Ultimate slave
Effects:
1º level fetishes just add a certain inclination to the character, basically likes and dislikes.
2º level fetishes start to heavily influence the character, for example if she becomes a foot master you won’t be able to get enough respect to be over little respect. You will have to pay a high cost so that she forgets her fetish to be able to solve the situation.
Even more level 2 fetishes have positive and negative effects:
- Public masturbation:
- The sister will walk in the nude and even openly masturbate in the house
- It will increase her sluttery stat
- She may masturbate outside the house and may be caught by other characters in the game (increasing their desire for her)
- Anal slut:
- She will prefer anal sex over vaginal sex
- She will always prefer that people cum inside her ass rather than outside
- If other characters have sex with her in the ass it will increase more her love for them
- Oral slut:
- She will prefer oral sex before penetration
- She will prefer people cumming within her mouth
- Other acts before penetration such as titjob, footjob, handjob won’t be used as much
- Foot master:
- Respect won’t increase anymore from the max amount of little respect
- She won’t lose dominant points that would make her fall to neutral attitude
- She will use her feet to humiliate the MC or to taunt him.
- She will prefer to use her foot before penetration acts
- She may expect foot worship in sex acts
- Dominatrix:
- It will increase the chance that she gets interested into sissy’s
- She will enjoy giving pain to her lover
- Only on special situations will she let others penetrate her
- She will prefer fucking people with a strap-on
- She may not let you cum until you beg
- She will scare all male characters that may be interested in her
- Slave
- She will enjoy pain
- She will enjoy being tied
- She will enjoy getting forced or raped
- She will enjoy servicing others
- Other characters will have it more easy to force her to have sex
- She may end up getting a hidden fetish (cheating fetish)
- She will fall in love easier with other characters
Level 3 fetishes are really intrusive and their effects are so expansive that only one of those may get the sister in each walkthrough:
- Public slut:
- The sister will enjoy public sex
- She will become more slutty
- She will have sex with anyone that wants to
- She will easily develop a love for gangbangs
- She won’t enter a relationship with anyone anymore and will break her current relationship
- It is really possible to end up pregnant without knowing the father
- Foot queen:
- Dominant points can’t fall from the high dominant level
- She won’t be interested in having sex with you
- She will make you worship her feet and obey her
- She won’t be interested in having any relationship with anyone other than you
- She will be free to do whatever she wants related to you
- She may humilliate you with her friends
- Sissy dominatrix:
- She will force you to be into chastity
- She will force you to dress girly
- She will fuck you in the ass with a strap-on
- She will make you service the strap-on
- She won’t be interested in having a relationship with any other character
- Ultimate slave:
- She will obey all your orders
- She will enjoy being used in any possible way
- She will live to serve
- She will be easily raped or conquered by other characters
- She will enjoy NTR be it her being taken away or having a girl have sex with you
- Very deviant
About attitude levels: They go from -100 to 100 being -100 totally submissive and 100 totally dominant, the levels are the following:
- -100 to -76: Totally submissive
- -75 to -50: Very submissive
- -50 to -25: Submissive
- -25 to -10: A little submissive
- -9 to 9: Neutral
- 10 to 25: A little dominant
- 26 to 50: Dominant
- 51 to 75: Very dominant
- 76 to 100: Totally dominant
About Sluttery: It goes from 0 to 100, the higher the more the girl wants to have sex, not having enough sex for her sluttery level will make the girl frustrated which will make it easier for others characters to fuck her and it will damage her current relationship. The levels are the following:
- 0 to 20: Normal
- 21 to 40: A little slutty
- 41 to 60: Slutty
- 61 to 80: Very slutty
- 81 to 100: Totally slutty
At very slutty and totally slutty the girl will cheat without being forced, she won’t be a loyal partner
Slutty will tend to cheat when frustrated.
Normal and a little slutty won’t cheat willingly.
Sluttery level increases by:
1º Having a lot of sex
2º Being a porn addict
3º Getting certain fetishes
4º Friends and relationships
5º Certain events or situations
P.D: This is quite complex, it's just to show a bit how to work over it.
-Fourth: Here is where you think about the events that you want to implement, storylines and making the characters that will be part of the game. Basically you make the characters, give them settings, objectives and how they act.
To not extend anymore will leave it at that.
-Fifth: Finally it's time to start making the game, first of all you need to make the system you wrote about, prepare the mechanics and stats and basically design the structure of what you want.
It is important to give it quite a bit of personalization so that it gives people a pleasant feeling while playing.
-Sixth: Incorporating the events, storylines and everything you wrote about, if you did all the points that I have said, you will have a really good structured game that won't require system chances or new mechanics. Everything you need already exists and you have to work upon that.
Here is where you can be more open in the sense of hearing your patrons or anyone that supports you. Do not concede a point of all the other points and explain clearly your idea to the people that want to support you. If you change the plans on points 1 to 5 the game will possibly be a failure because it may end up as a mess.
