Is there any walkthrough? Or we just keep talking and peeping the heroine everynight to progress the story?
The gameplay is really that dumb, yeah. The scenes get unlocked in batches based on the heroine's stats.
There are two stats: Affection (character-specific: towards MC or the two other brats) and Lewdness (general). For example, 10 MC Affection and 10 Lewdness will unlock a batch of 2 scenes for MC, 20 MC Affection & 20 Lewdness will unlock another batch of 2 scenes, and so on.
The stats get accumulated only via the player's actions, i.e. there is no passive increase while roaming/skipping events.
Some "Talk" options will increase the heroine's affection towards MC, while the other will increase the Lewdness.
The "Action" option (e.g. "Take a class" or "Help at the barn") will either increase the MC Affection or trigger a scene if the stats threshold is met.
When a brat is talking to a heroine, chasing him off will increase the heroine's affection towards MC, while letting them continue will either increase the heroine's Affection towards the brat or her Lewdness.
The shower peeping will increase the heroine's Lewdness by 2. The scene is always the same.
I'd recommed skipping day/night cycles via the glowing star at the down-right corner of the map, rather than going to sleep. It will save your time without any ramifications.
Personally, I'd say the gameplay here is rather an obstacle to get through the scenes than some meaningful element of the game. It's really dull and boring. The developers were kind enough to add a button that maximizes all the stats (in the shrine location at the top-center of the map) - you just have to go to the right places at the right time and trigger the scenes you want (but it still get unlocked in order for each character). You should absolutely go for it, as the gameplay adds
nothing to support the buildup necessary for a decent NTR and/or character development.