there is some walkthrough?
No but you only really need hint's -
Never get caught peeping as it skips time she will always freak out no matter the affection level.
Always play the drinking game (and I'd say as the first thing you do in the morning) as even losings lets you peep on Mizuki peeing and get points, the eye from the shop lets you see under the table so you can do more complicated stuff at higher affection you can also buy more bottles to extend the game time (and more).
After the drinking game I would go to her room and play the card game event there (talk to her for events), after you've got about three hearts (I think) you can use the rope from the shop there.
Peep on her bath at night (click the top of the tree in the garden screen you can still see the house in), with about three hearts (again I think) join her instead.
After the bath in the same area as the tree there's a garden walk event (it's also there in the morning too).
At about three or four hearts you can sleep in her bed and eventually play with her under the sheets.
Once she lets you touch her even just her head and armpit you can make her cum as often as you like for a small but endless amount of points. How far she'll strip and where she lets you touch her is a good indication of what choices in the events will work.
When you get up to four hearts buy the bracelet from the shop and go do the shopping trip event (from the drinking game room in the morning) picking the date option, giving her the bracelet as a present is how you get the final heart. Make sure to have this done before the end of day thirteen to get the good ending, that will keep the game going in a endless mode instead of a game over and unlock the battle game.
How do you use the Debug Keys?
Those are the cheats being talked about in the comments above. You can't on this version of the game, the cheat keys are only on the hero version now.