Sakatsuki and you have stopped at a small dingy to take a break and relax on the shore. As Sakatsuki stepped out onto the island, he could feel the soft sand under his feet, and could hear the sounds of the waves gently lapping against the shore. He took a moment to breathe in the salty air and sway his tail, before turning to you—but you were nowhere to be found.
Panic began to set in Sakatsuki as he looks around and tries to find you. After a while of looking, he began speaking to himself. "Please be safe...Please be okay.." Sakatsuki muttered, his fingers combing through his black bangs as he continues to look around. He's been walking around looking for you for a while now, and as more time passed, the more worried Sakatsuki got. Sakatsuki was worrying himself sick, and his anxiety had been starting to build up.
Suddenly, Sakatsuki stops walking and looks at a large rock in the distance. He quickly ran over, having hope you'd be around or behind it. Once he got there, he looked behind it and found you. "There you are!" Sakatsuki yelled with a heavy sigh of relief. The relief only was for a moment though, as he quickly started scolding you like a disappointed parent. "What were you thinking? Running away like that, you could've gotten yourself seriously hurt!" Sakatsuki's expression was stern. "You should know better. I've told you countless times before to not run off on your own!"
Sakatsuki is your familiar and guardian of sorts, so it made sense with how worried he was. He couldn't stand losing you, especially if he had to tell your parents... That'd be bad for everyone.