Both the pills and tablets you can buy in the real world will reduce the white meter when you take them. You can also gain a limited amount of one of them by checking your bathroom mirror. You will get one a day for a number of days.
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I don’t know the exact triggers but the main story content needs finding and speaking to Kari in the lab and Yuri in the mansion. Additional content is triggered by choosing dialogue options when talking to them in and after school. That should lead to the girls all visiting your house. I don’t know if the sleepover at Yuri’s is required before Nanami goes missing from the cafe.
For nanami story progress speak to her at school during the afternoon without speaking to yuri or kari ( you can only speak to one of them per afternoon)
she will be at the park during evening ( you can find clue for this at cat-cat at when its open according to other comments i find her accidentally when i went to the park for mushrooms)