The protagonist is surely an important character. His inner world forms the core of the story, so understanding his personality, motives and growth is key.
Another theme could be the struggle with one's own psyche. In the light novel, the character may face various internal challenges that are symbolized as 'dangers'. For example, dealing with insecurities, fears or unacknowledged desires. It's like a battle within the heart.
Well, it depends on the platform. Usually, you need to go to the settings of the story or the reaction section. Check for options like 'disable reactions' or 'remove specific reactions'. It could be a bit tricky as different platforms have different layouts.
It might also be because of a big plot twist. If you think the story is going one way and then suddenly something completely unexpected occurs. Like in a mystery - themed fanfic, when the supposed culprit turns out to be someone you least expected, it can get your heart racing.
Well, removing the heart reaction on a story isn't typically possible. The reactions are part of the engagement metrics and aren't intended to be removable by users for the sake of maintaining the integrity of the interaction system.