bare bones basics walk through for both the new 3d monthly update but most of this should work on the Old 2D build just that there are some new features and events on the 3d while missing some of the old sex scenes and what not. Now I do use the cheat plug in for infinite energy and money, for the first two shifts, am and noon, all I do is work out since I dont need to worry about money and cleanliness, and at the 3rd time slot at eve, I go to the store and buy everything, I do this because some items are only available later in the day begging later on in the game so to keep the daily cycle simple these are the steps.
Only exception are the weekends events can vary.
The first thing you should do once you are with the sister is to get the favorability up, the best way i've done it is to interact with her both times at dusk and then night, both times you gift her sweets and then rub her head for +4 favorability, do this every night until you get to 50. You should reach this at night on the 5th day after the usual rubbing head and gifting sweets, at this point, you can click on her chest as an interaction, before she would tell you to stop but now she allows you and every 3 clicks she gains sexual curiosity, you can click on her 9 times to get +3 to her total.
On the Weekends, after the very first morning shift, your sister will be on the couch and you can click on her to spend time with her to gain favorability, depending on what choice you make on these random events either her favorabilty or sexual curiosity goes up, and then once eve hits you can go shopping and for the new build you can buy the sex book for later on.
For each night, on both times you can interact with her, you keep doing the same gift her sweets, rub head and then click on the chest 9 times for +4 favorabilty and +3 sexual curiosty, there is an event on the 8th day at night where you walk on her sleeping on the couch, have fun if you want there is no punishment even though the game trys to make you 2nd guess yourself 3 times
On the 9th day you should have 70+ favorability with her so you should be able to take a bath with her and now this is what we will be doing every time at the 4th time slot at dusk.
On the 10 day at dusk I got prompted to keep a cat, it makes the cleanliness go down twice as fast but since I'm using the cheat plug in it does affect us so just say yes to raise the favorability up with your sister, after that it jumps to the last time slot at night so just once again interact with a gift and click the usual spot like usual.
Then going back to the normal cycle of asking for your sister to take a bath with you at dusk, For the first 3 times we wont be able to do much except read the interaction but after the first time you get the choice between two options, keep picking the top saying you would like to rub her breast and then after 3 times of bathing with her she allows you and like before when youre gifting her sweets, you click on her chest 3 times but this time its +3 after every 3 clicks so this is our main way to raise sexual curiosity, getting +9 each time.
The only time you cannot do this is on weekends where she takes a bath ahead of you at dusk so you can just interact with gifts or start learning if you would like.
Once you get your favorabilty at 100 you can swap the gift from sweets to the manga and focus only on sexual curiosty, and in the new build you can educate her sexual knowledge as well, currently the only thing you can do is get the knowledge up to 100% and then that makes the other stats raise even faster but the only other stat there is the bottom, where we need a 30% to be able to have sex with the sister when you interact with her while reaching the other requirments, 70 fav, 30 bottom knowledge, and having a condom on you.
There's more to explore like eventually you can night crawl with a book, have sex in the bath, there is a shady shop that you can talk to the lady in a future build to touch her and stuff, but thats the very basics, in the old build once you get your stats up you can play around with the lust potion and the hypnotizing coin and there's more items for different scences as well but I don't want spoil each sex scene. Just leave saves as early as you can when reaching high stats on the old build to find the different sex scenes because it does some times ask you to do the same thing multiple times to find all the scenes like using the sleeping pills if i remember correctly. I am mostly just saying this because I haven't played the old build in months sorry