THIRD: you can only get 6 white hearts, it wont go any further, no matter what I do.
Can you check it out if that happens to you?
It's a bit labor-intensive, but possible. Moreover, even with 4 red hearts, you can get 7 white ones. (Or maybe even earlier, I haven't tested it.)
With the Horror Videotape, you can trigger 2 scenes in a row within 1 in-game day. You can get 2 white hearts in 1 scene. Let me summarize. You can get 4 additional white hearts daily, but each new in-game day, the 2 white hearts if you have 4 red hearts (with more red/purple hearts, something might be different.).
This cumulative system can display a maximum of 7 white hearts, but judging by the "White Hearts" variables, they accumulate beyond the display limit.
Now, a little "guide." To get the Videotape, I would recommend collecting 2 Tarot cards: [Chariot] and [Death].
After obtaining these 2 cards, go to the starting location and rest at the bonfire next to the [Cat-Maid Swordswoman]. This creates an autosave (it moves the game time forward slightly, but no more than 2 hours). After the autosave, go to the "Trash Can" (or its ruins) and use the Chariot card. A van arrives and unloads the goods for everyone to see. If you don't have a video tape, press F5 (reset game, keep in mind that any unnecessary player movements may cause the autosave to overwrite, and you'll have to start over from the bonfire on another game day). After restarting the game load the autosave at the campfire, and repeat. As soon as you have a video tape (or another necessary item, such as a [Fan] for hot days), summon the [Death] Tarot card and run to the milk vending machine. After the red screen flashes, go and collect all the goods for free, and don't forget to pick up the [Cat's Paws].
Now that you have a video tape, you can trigger the necessary scene. But before doing so, you must give Imouto the potion from the 1-st fragment of the Philosopher's Stone. Otherwise, Imouto will fall asleep after 10:00 PM. To trigger the two scenes in sequence, you need to carefully monitor the game time. One scene with 2 hearts takes 30 in-game minutes, and after 11:00 PM, watching TV is no longer possible. In other words, to get 4 hearts in 1 day, you can't start the first scene later than 10:29 PM (otherwise, you'll only have enough game time for 1 scene or 2 white hearts). You can save immediately after the 1-st scene, but you can't do anything other than start the 2, otherwise Imouto will most likely fall asleep.
And I almost forgot, in the scenes themselves: after each "filling" animation, you must hover your mouse over Imouto and then move your mouse away from it to another location on the screen. This triggers the Imouto status display and the scripts for "adding" different hearts. If you forget to do this, you might not add any hearts at all in one scene.
So, for 4-5 consecutive, correctly played game nights, you can earn 7+ white hearts.
