Thanks for your hard work, and especially thank you for that final note on the walkthrough! I did as you suggested and played the game without it (actually, I only even opened the walkthrough after I played). A couple things stood out to me:
1) I don't mean any offense, but you could use a proofreader. Your spelling is generally fine, but the grammar... I assume English is not your native language?
2) While playing with NTR on, I chose not to have Miru accept her ex's modeling job (she seems like a more action-oriented and rebellious girl, so I didn't think she'd be all that interested in doing a "do exactly what you are told" and "hold that pose" job like being a model - I get it's a setup for NTR, but I only turned on NTR as a challenge and the fact that this job seemed out-of-character made it an easy choice to pass up). That being said, even if she turns down the modeling job she winds up in her ex's car... on her way to the modeling job. Er, what? Why?
3) I don't see any reason to be nice to Katie. Your setup for the enmity between the siblings is solid - so solid, in fact, that it seemed perfectly natural to insult her at every turn. It felt like the game wanted me to be nice to Katie, since it gave me every opportunity to do so... but it never actually gave me a reason to be nice to her. The MC thought she was a cunt, and that's exactly what she was. I think the obvious assumption is "The player is horny and will expect kindness to get them laid, so they'll be kind", and while that's generally a safe assumption to make, it doesn't make for quality storytelling. Just give me a glimmer of a sweet side earlier on, pretty please! Otherwise it feels like the "canon" route is actually bullying her every chance you get (props for keeping this in there as a route and not straight railroading the player, at least).
4) I find it interesting that the player controls Miru every once in awhile. Cool choice, even if I generally avoid female protag games. This feels like a neat sort of middle ground. Bonus points for making Miru's story intriguing!
5) The MC got the shit kicked out of him in prison, and then, after a day in the hospital, went camping? This is not really a big deal, but damn the MC's body would ache. If he fucks anyone at the campground, I expect he'd be the one screaming louder than the girl... and it would be in pain, not pleasure lol. Still, since this is only one path out of prison, I don't expect any big changes. Maybe just a mention? Like a comment from the MC about still being sore or something.
All in all, it's a cool game. I'm impressed by the amount of relationships you've managed to fit in here, though there is clear emphasis on Miru and Katie - I hope the rest of the cast gets lots of time to shine too! I'll go back and play a couple more times to set up some different routes - I'm looking forward to where things are headed. Keep doing what you're doing, there's definitely lots of potential here! Best of luck, and I hope you have a great day!