There’s an existing guide that provides the exact steps. I created this guide to try and explain more how the endings are arranged and how your choices determine endings, rather than the specific steps.

The hearts measure Haru’s emotional state rather than physical health. Hearts are lost when choosing options that are uncomfortable or emotionally draining. Some options become unavailable when you run low on hearts. Running out of hearts does not trigger a game over, but does affect the Good End and Bad End.

There are two personal scenes that Haru can have with her friends. Having one of these scenes means you’ll get one of the endings relating to that character.

You can only see one personal scene during the story. As Erika’s comes first, you’ll have to tell her you’re too tired to talk with her in order to get the scene with Manami.

This occurs when Haru, Erika, and Manami go back to their room after bathing. After the meal, Erika will ask if you mind having a chat. If you agree, you'll get one of the two Erika Endings.

If you go to the baths with her, you get Erika End #2. If you don't go to the baths, you get Erika End #1.

To get the personal scene with Manami, you have to choose not to have a chat with Erika. Erika will go to the baths on her own, and then Manami will suggest you keep her company for a bit. If you do, you'll get one of the two Manami endings.

If you give her the present, you get Manami End #2. If you don't, you get Manami End #1.

If you don't keep Manami company, you'll get either the good or bad ending.

These are endings where you do not have a personal scene with Erika or Manami.

The Normal End is achieved by turning down Manami's suggestion of going to the hot springs. This gets you an ending where they go to a theme park instead.

The good and bad endings are achieved by skipping the personal scenes of both Erika and Manami.

If you have any hearts left by the end, you get the Good End, and if your hearts are all empty, you get the Bad End.