Daiki adores his older sister and Kamiya is a gloomy guy whome Daiki thought was his sister's boyfriend. When Daiki confronted Kamiya, he realized he was wrong and they became friends instead. Then, the two fell in love and was able to confess to each other. But that's just chapter 1. From ch2 to 4, the couple struggles to communicate and handle their thoughts. They rarely talk about their issues and Kamiya's rejection always made Daiki walk on eggshells while he tries to control his urges as the younger and more confident guy in the relationship.
[I must be "too old" for this impulsive yet full of overthinking trope. I will do my best to avoid them instead.]
more than red